Fix compilation of kotlin-maven-plugin

Also remove the remaining usage (in a comment) of
JvmAbi.DEFAULT_MODULE_NAME

core/metadata.jvm/src/jvm_metadata.proto

@@ -119,7 +119,7 @@ extend TypeParameter {
 }
 
 extend Class {
-  // If absent, assumed to be JvmAbi.DEFAULT_MODULE_NAME
+  // If absent, assumed to be "main" (JvmProtoBufUtil.DEFAULT_MODULE_NAME)
   optional int32 class_module_name = 101 [(string_id_in_table) = true];
 
   repeated Property class_local_variable = 102;

core/metadata.jvm/src/org/jetbrains/kotlin/metadata/jvm/JvmProtoBuf.java

@@ -3933,7 +3933,7 @@ public final class JvmProtoBuf {
    * <code>extend .org.jetbrains.kotlin.metadata.Class { ... }</code>
    *
    * <pre>
-   * If absent, assumed to be JvmAbi.DEFAULT_MODULE_NAME
+   * If absent, assumed to be "main" (JvmProtoBufUtil.DEFAULT_MODULE_NAME)
    * </pre>
    */
   public static final