Get rid of 'class object' usages in code and builtins

Replace some comments and library usages as well

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

@@ -25,7 +25,7 @@ import org.jetbrains.kotlin.resolve.scopes.JetScope
 import org.jetbrains.kotlin.types.JetType
 
 public trait SamConversionResolver {
-    public class object EMPTY : SamConversionResolver {
+    public companion object EMPTY : SamConversionResolver {
         override fun <D : FunctionDescriptor> resolveSamAdapter(original: D) = null
         override fun resolveSamConstructor(name: Name, scope: JetScope) = null
         override fun resolveFunctionTypeIfSamInterface(

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

@@ -22,7 +22,7 @@ import org.jetbrains.kotlin.name.Name
 // The purpose of this class is to hold a unique signature of either a method or a field, so that annotations on a member can be put
 // into a map indexed by these signatures
 data class MemberSignature private(private val signature: String) {
-    class object {
+    companion object {
         platformStatic public fun fromMethodNameAndDesc(nameAndDesc: String): MemberSignature {
             return MemberSignature(nameAndDesc)
         }