Avoid scanning pre-installed APEX twice during boot sequence

Now that we can retrieve ApexFiles from ApexFileRepoitory we don't
have to scan apex files in ScanAndGroupApexFiles, which is called
on every boot.

Bug: 179497746
Test: atest ApexTestCases
Change-Id: Ib70a38c8b35bdb82dd6b31b6dd9662f9d815de1b
6 files changed