Fix warnings when compiling repl

Author: WojciechMazur

repl/src/dotty/tools/repl/AbstractFileClassLoader.scala

@@ -43,7 +43,7 @@ class AbstractFileClassLoader(root: AbstractFile, parent: ClassLoader, interrupt
     else defineClass(name, bytes, 0, bytes.length)
   }
 
-  def defineClassInstrumented(name: String, originalBytes: Array[Byte]) = {
+  private def defineClassInstrumented(name: String, originalBytes: Array[Byte]) = {
     val instrumentedBytes = ReplBytecodeInstrumentation.instrument(originalBytes)
     defineClass(name, instrumentedBytes, 0, instrumentedBytes.length)
   }

repl/src/dotty/tools/repl/ReplBytecodeInstrumentation.scala

@@ -6,9 +6,9 @@ import scala.language.unsafeNulls
 import scala.tools.asm.*
 import scala.tools.asm.Opcodes.*
 import scala.tools.asm.tree.*
-import scala.collection.JavaConverters.*
+import scala.jdk.CollectionConverters.*
 import java.util.concurrent.atomic.AtomicBoolean
-  
+
 object ReplBytecodeInstrumentation:
   /** Instrument bytecode to add checks to throw an exception if the REPL command is cancelled
    */