Fix jarjar rules for feature flags

This tightens up the jarjar rule that was added to avoid failures in
CtsStrictJavaPackagesTestCases due to duplicated flag classes. The
original rule was also causing the flag names themselves to be renamed,
resulting in incorrect (always false) values being returned.

Bug: 319515313
Test: atest CtsStrictJavaPackagesTestCases
Change-Id: I9147825fdbe3a392897587c7fadf17eb7736295a