Revert "add isKotlinSourceElement method to Source interface in order to recognize kotlin source elements during compilation"

This reverts commit c342f6870a.

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/kotlin/KotlinJvmBinarySourceElement.kt

@@ -19,6 +19,5 @@ package org.jetbrains.kotlin.load.kotlin
 import org.jetbrains.kotlin.descriptors.SourceElement
 
 public class KotlinJvmBinarySourceElement(public val binaryClass: KotlinJvmBinaryClass) : SourceElement {
-    override fun isKotlinSourceElement(): Boolean = false
     override fun toString() = javaClass.name + ": " + binaryClass.toString()
 }