Consolidate ANR Rate Docs

[philipphofmann]

Problem Statement

The Android docs have two different places for ANRs. One explaining ANRs in detail and another one about the ANR rate, which is part of the performance metrics. This doesn't make sense.

Solution Brainstorm

Move the ANR rate docs from the performance metrics to the ANR docs.

[linear]

DOCS-2256 Consolidate ANR Rate Docs