remove @ExperimentalCoroutinesApi from testCoroutineScheduler

`TestDispatcher` used to be experimental, but it is not any more Kotlin/kotlinx.coroutines#3622

Author: aSemy

kotest-framework/kotest-framework-api/src/commonMain/kotlin/io/kotest/core/test/delayController.kt

@@ -7,12 +7,10 @@ import kotlinx.coroutines.test.TestDispatcher
 import kotlin.coroutines.CoroutineContext
 
 @ExperimentalStdlibApi
-@ExperimentalCoroutinesApi
 val TestScope.testCoroutineScheduler: TestCoroutineScheduler
    get() = coroutineContext.testCoroutineScheduler
 
 @ExperimentalStdlibApi
-@ExperimentalCoroutinesApi
 val CoroutineContext.testCoroutineScheduler: TestCoroutineScheduler
    get() = when (val dispatcher = this[CoroutineDispatcher]) {
       is TestDispatcher -> dispatcher.scheduler