JVM_IR: Fix check for whether classes are from Java.

This allows us to not generate redundant immutable collection
stubs. The code to generate the immutable collection stubs does
not deal well with thinking that all external declarations
come from Java.

compiler/testData/codegen/box/toArray/toArrayShouldBePublicWithJava.kt

@@ -1,5 +1,4 @@
 // IGNORE_BACKEND_FIR: JVM_IR
-// IGNORE_BACKEND: JVM_IR
 // TARGET_BACKEND: JVM
 // WITH_RUNTIME
 // IGNORE_LIGHT_ANALYSIS