Drop the default apex_available value from BUILD files

If apex_available is missing from Android.bp files, ApexAvailable
returns [//apex_available:platform], which is the default. To avoid
BUILD file verbosity, remove the build system default value from the
generated BUILD files.

Bug: 277651159
Test: go test ./bp2build

Change-Id: I4129c2a93ac28578f46ebeed49baa23ce727aa1f

android/mutator.go

@@ -747,7 +747,13 @@ func ApexAvailableTags(mod Module) bazel.StringListAttribute {
 		// TODO(b/218841706): hidl_interface has the apex_available prop, but it's
 		// defined directly as a prop and not via ApexModule, so this doesn't
 		// pick those props up.
-		attr.Value = ConvertApexAvailableToTags(am.apexModuleBase().ApexAvailable())
+		apexAvailable := am.apexModuleBase().ApexAvailable()
+		// If a user does not specify apex_available in Android.bp, then soong provides a default.
+		// To avoid verbosity of BUILD files, remove this default from user-facing BUILD files.
+		if len(am.apexModuleBase().ApexProperties.Apex_available) == 0 {
+			apexAvailable = []string{}
+		}
+		attr.Value = ConvertApexAvailableToTags(apexAvailable)
 	}
 	return attr
 }