PrintManagerService: Don't prune services on all package change events.

We should only need to prune services if the package that changed
had a print service or has been changed to have a print service.

Bug: 63019430
Test: Manual; observed that the print spooler isn't started up.
Test: run cts -m CtsPrintTestCases

Change-Id: I32df27e4b1d11615cf6053dd3d35c2b60068d0d3