Deprecate CellLocation#requestLocationUpdate

Remove this method, which is undesirable, has unfortunate
side effects, and which is a worse way of getting the current
location than other methods such as TelephonyManager#getAllCellInfo()
(since KK) and TelephonyManager#requestCellInfoUpdate() (since QT/11).

Bug: 152648516
Test: make update-api && make (docstring-only change)
Change-Id: I3c7d345abcdd8c35cf539d33166ddf76ba987b1c