ContextHubService: Don't double report app loads

Our logs would show us loading apps twice, when in reality we
load them once, and then update our caches with the app
version later.

There are other issues around how this code works (for example,
b/30970527), but this is an appropriate approach at this
stage of the release.

Bug: 30836667
Change-Id: I2e2a65bc8a2ef4d1703df0a0586a8ed251607af7