Clear UIDs when sharing NetworkCapabilties for ConnectivityDiagnostics.

ConnectivityDiagnostics shares NetworkCapabilities in
ConnectivityReports and DataStallReports. These NetworkCapabilities need
to have their UIDs scrubbed before they are shared with callbacks.

Bug: 148942124
Test: atest FrameworksNetTests
Change-Id: I5bde5a8116f7e36b8f4de49adf4cab8ec45a5aa4