Doc: replace "Start Android AVD Manager" with "Start AVD Manager"

The UI text changed, because "AVD" means "Android Virtual Device":
7d266c648efc90871201c63c3119d8437f8cebe6.

Change-Id: I9f581a5c580f38880398d0e3aed35db5fd140b98
Reviewed-by: Daniel Teske <daniel.teske@digia.com>