[pm] feature flag is not needed for MATCH_UNINSTALLED_PACKAGES

The behavior of the flag used in API methods such as getPackageInfo will
stay the same. The only change is the installed state which is hidden. No
need to use a feature flag.

This CL is needed for the installed state change CL to proceed.

BUG: 288142708
Test: atest
android.content.pm.cts.PackageManagerTest#testUninstallWithKeepData

Change-Id: I319ad2d948b3c0d58468387b9b5ab4b9b48ad70a