Revert "Qualify prebuilt_etc apex module name by relative paths"

This reverts commit d94cccc523a9e8395bd902298827bc62061222cb.

Reason for revert: Patchset 2 was wrong, doesn't actually fix the bug

Change-Id: Ie2d931ad3e2277ce1923284b13f50f62ac2f8917
diff --git a/apex/apex.go b/apex/apex.go
index 99a0da8..9a80ec6 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -1636,7 +1636,7 @@
 
 func apexFileForPrebuiltEtc(ctx android.BaseModuleContext, prebuilt prebuilt_etc.PrebuiltEtcModule, outputFile android.Path) apexFile {
 	dirInApex := filepath.Join(prebuilt.BaseDir(), prebuilt.SubDir())
-	return newApexFile(ctx, outputFile, strings.ReplaceAll(outputFile.Rel(), "/", "_"), dirInApex, etc, prebuilt)
+	return newApexFile(ctx, outputFile, outputFile.Base(), dirInApex, etc, prebuilt)
 }
 
 func apexFileForCompatConfig(ctx android.BaseModuleContext, config java.PlatformCompatConfigIntf, depName string) apexFile {