Revert "Allow libz to have stub even though it's not an LLNDK li..."

Revert submission 1312595-zlib_as_stub

Exempt-From-Owner-Approval: reverting a bad change

Reason for revert: broke rvc-dev-plus-aosp
Reverted Changes:
I7c0a7f954:libz is a stub
If51a7e80f:libz provides stubs to Mainline modules.
I26417bb78:Allow libz to have stub even though it's not an LL...

Change-Id: I617eb90a33eacc7f264551c969ff5a16fa0d4087

cc/vndk.go

@@ -309,12 +309,7 @@ func processVndkLibrary(mctx android.BottomUpMutatorContext, m *Module) {
 		panic(err)
 	}
 
-	if m.HasStubsVariants() && name != "libz" {
-		// b/155456180 libz is the ONLY exception here. We don't want to make
-		// libz an LLNDK library because APIs required for vendors might be
-		// wider than what we expose as NDK/Mainline APIs. As the library is
-		// an external one, it's risky to keep the API stability promise if
-		// it becomes an LLNDK.
+	if m.HasStubsVariants() {
 		mctx.PropertyErrorf("vndk.enabled", "This library provides stubs. Shouldn't be VNDK. Consider making it as LLNDK")
 	}