Enable JVM IR for stdlib/reflect/test libraries

Changes in Gradle integration tests are needed because:
- in new-mpp-android, kotlin-stdlib-jdk8 is used, and JVM IR generates
  JDK 8-specific bytecode (invokedynamic). D8 needs to be configured to
  desugar it with source/target versions set to 1.8, otherwise it
  reports an error.
- in AndroidExtensionsManyVariants and AndroidIcepickProject, D8 fails
  with assertions enabled if AGP < 4.0.0 is used because of
  https://issuetracker.google.com/issues/148661132. The tests which use
  old AGP versions are probably not relevant anymore anyway.

Changes in kotlin-stdlib-runtime-merged.txt are caused by a slightly
different generation scheme of collection subclasses in JVM IR, and are
harmless.

(Previous attempt was at 15e978dbd311c2ba78ec32b394c21acde9811ccb.)

dependencies/kotlin-build-gradle-plugin/src/BuildProperties.kt

@@ -80,8 +80,6 @@ class KotlinBuildProperties(
 
     val localBootstrapPath: String? = getOrNull("bootstrap.local.path") as String?
 
-    val useIRForLibraries: Boolean = getBoolean("kotlin.build.useIRForLibraries")
-
     val useFir: Boolean = getBoolean("kotlin.build.useFir")
 
     val useFirForLibraries: Boolean = getBoolean("kotlin.build.useFirForLibraries")