We no longer need to support fallback packages and need to migrate them
back to being enabled (but only once, to allow the user to disable them
manually later). This CL:
1) Removes the logic which enables/disables packages and the test cases
which only cover the enabling/disabling logic.
2) Checks at boot time if the fallback logic is enabled; if so, it
re-enables the fallback package if one exists and then disables the
fallback logic permanently.
3) Amends remaining test cases to use "primary" and "secondary" instead
of primary/fallback, to keep testing that higher priority packages
are more preferred without involving the fallback behaviour.
4) Fixes a bug in the package selection logic that would not have
triggered in the previous setup (as our production configs never had
more than one available-by-default, non-fallback packages) that was
revealed by one of the modified test cases: the boot time logic to
reset the user's setting if their previously chosen provider was no
longer available triggered even if the user had not actually chosen a
provider, causing the automatically selected provider to be
considered a manual user choice, and preventing a higher priority
provider from being automatically chosen if it later becomes
available.
Bug: 126588129
Test: atest WebViewUpdateServiceTest
Change-Id: I532c0faae2427de7132f716725bf62e256975410
ef47890d65