Clean up global search and web search activity finding

This removes the '*' value for android.app.searchable and
android.app.default_searchable that was previously used by apps to say
that they want global search as their search. I think the only
activity that this will affect is the wallpaper chooser in the
launcher, which doesn't seem like it matters.  It could mean that some
third party code will stop invoking global search, but all they would
need to do is call startSearch() with globalSearch=true instead.

Fixes http://b/issue?id=2377433 and http://b/issue?id=2377429

Change-Id: I0252952b44ae85dab31221b598ed79cc24e2b580