Remove obsolete CommonPool support

kotlinx-coroutines-core/common/src/CoroutineContext.common.kt

@@ -12,8 +12,6 @@ import kotlin.coroutines.*
  */
 public expect fun CoroutineScope.newCoroutineContext(context: CoroutineContext): CoroutineContext
 
-internal expect fun createDefaultDispatcher(): CoroutineDispatcher
-
 @Suppress("PropertyName")
 internal expect val DefaultDelay: Delay
 

kotlinx-coroutines-core/js/src/CoroutineContext.kt

@@ -12,7 +12,7 @@ private external val navigator: dynamic
 private const val UNDEFINED = "undefined"
 internal external val process: dynamic
 
-internal actual fun createDefaultDispatcher(): CoroutineDispatcher = when {
+internal fun createDefaultDispatcher(): CoroutineDispatcher = when {
     // Check if we are running under jsdom. WindowDispatcher doesn't work under jsdom because it accesses MessageEvent#source.
     // It is not implemented in jsdom, see https://github.com/jsdom/jsdom/blob/master/Changelog.md
     // "It's missing a few semantics, especially around origins, as well as MessageEvent source."

kotlinx-coroutines-core/jvm/src/CoroutineContext.kt

@@ -9,19 +9,6 @@ import kotlinx.coroutines.scheduling.*
 import kotlin.coroutines.*
 import kotlin.coroutines.jvm.internal.CoroutineStackFrame
 
-internal const val COROUTINES_SCHEDULER_PROPERTY_NAME = "kotlinx.coroutines.scheduler"
-
-internal val useCoroutinesScheduler = systemProp(COROUTINES_SCHEDULER_PROPERTY_NAME).let { value ->
-    when (value) {
-        null, "", "on" -> true
-        "off" -> false
-        else -> error("System property '$COROUTINES_SCHEDULER_PROPERTY_NAME' has unrecognized value '$value'")
-    }
-}
-
-internal actual fun createDefaultDispatcher(): CoroutineDispatcher =
-    if (useCoroutinesScheduler) DefaultScheduler else CommonPool
-
 /**
  * Creates context for the new coroutine. It installs [Dispatchers.Default] when no other dispatcher nor
  * [ContinuationInterceptor] is specified, and adds optional support for debugging facilities (when turned on).

kotlinx-coroutines-core/jvm/src/Dispatchers.kt

@@ -29,7 +29,7 @@ public actual object Dispatchers {
      * Level of parallelism X guarantees that no more than X tasks can be executed in this dispatcher in parallel.
      */
     @JvmStatic
-    public actual val Default: CoroutineDispatcher = createDefaultDispatcher()
+    public actual val Default: CoroutineDispatcher = DefaultScheduler
 
     /**
      * A coroutine dispatcher that is confined to the Main thread operating with UI objects.

kotlinx-coroutines-core/jvm/test/TestBase.kt

@@ -199,15 +199,12 @@ public actual open class TestBase(private var disableOutCheck: Boolean)  {
     }
 
     fun initPoolsBeforeTest() {
-        CommonPool.usePrivatePool()
         DefaultScheduler.usePrivateScheduler()
     }
 
     fun shutdownPoolsAfterTest() {
-        CommonPool.shutdown(SHUTDOWN_TIMEOUT)
         DefaultScheduler.shutdown(SHUTDOWN_TIMEOUT)
         DefaultExecutor.shutdown(SHUTDOWN_TIMEOUT)
-        CommonPool.restore()
         DefaultScheduler.restore()
     }
 

kotlinx-coroutines-core/jvm/test/knit/TestUtil.kt

@@ -26,7 +26,6 @@ private val OUT_ENABLED = systemProp("guide.tests.sout", false)
 fun <R> test(name: String, block: () -> R): List<String> = outputException(name) {
     try {
         captureOutput(name, stdoutEnabled = OUT_ENABLED) { log ->
-            CommonPool.usePrivatePool()
             DefaultScheduler.usePrivateScheduler()
             DefaultExecutor.shutdown(SHUTDOWN_TIMEOUT)
             resetCoroutineId()
@@ -39,15 +38,13 @@ fun <R> test(name: String, block: () -> R): List<String> = outputException(name)
             } finally {
                 // the shutdown
                 log.println("--- shutting down")
-                CommonPool.shutdown(SHUTDOWN_TIMEOUT)
                 DefaultScheduler.shutdown(SHUTDOWN_TIMEOUT)
                 shutdownDispatcherPools(SHUTDOWN_TIMEOUT)
                 DefaultExecutor.shutdown(SHUTDOWN_TIMEOUT) // the last man standing -- cleanup all pending tasks
             }
             checkTestThreads(threadsBefore) // check thread if the main completed successfully
         }
     } finally {
-        CommonPool.restore()
         DefaultScheduler.restore()
     }
 }

kotlinx-coroutines-core/native/src/CoroutineContext.kt

@@ -25,7 +25,7 @@ internal actual object DefaultExecutor : CoroutineDispatcher(), Delay {
 
 internal fun loopWasShutDown(): Nothing = error("Cannot execute task because event loop was shut down")
 
-internal actual fun createDefaultDispatcher(): CoroutineDispatcher =
+internal fun createDefaultDispatcher(): CoroutineDispatcher =
     DefaultExecutor
 
 @SharedImmutable