Define a new config key for the recommendation provider app.

Created a new config key and removed the previous key that
was defined in default.xml. Also removed the SettingsProvider logic
as we'll set the default in NetworkScoreService in a follow-up CL.

Bug: 35095406
Test: build and install.

Change-Id: I2893be31fd526af8a66d6d1b7d8978adf7e32c0f