Blacklist SystemProperties again

SystemProperties leads to a dottydoc failure, so stays blacklisted
for now. It does pass the normal compile-stdlib test.

Author: odersky

compiler/test/dotc/scala-collections.blacklist

@@ -56,3 +56,6 @@
 
 ../scala-scala/src/library/scala/util/control/TailCalls.scala
 # -Ycheck:classOf failure
+
+#../scala-scala/src/library/scala/sys/SystemProperties.scala
+# Test dotty.tools.dottydoc.TestWhitelistedCollections.arrayHasDocumentation failed

compiler/test/dotc/scala-collections.whitelist

@@ -400,9 +400,8 @@
 
 ../scala-scala/src/library/scala/compat/Platform.scala
 
-../scala-scala/src/library/scala/sys/SystemProperties.scala
 ../scala-scala/src/library/scala/sys/package.scala
-../scala-scala/src/library/scala/sys/SystemProperties.scala
+#../scala-scala/src/library/scala/sys/SystemProperties.scala
 ../scala-scala/src/library/scala/sys/Prop.scala
 ../scala-scala/src/library/scala/sys/PropImpl.scala
 ../scala-scala/src/library/scala/sys/BooleanProp.scala