SensorService: Fix some warnings

For build-system CFLAGS clean-up, remove unused variables.

Also fix some warnings related to format strings, and signed
comparisons.

Bug: 18632512

(cherry picked from commit d4036b6b7f9609fe09efabdbfbb8c8f9428f76f7)

Change-Id: I5e48dce36678c12069c0e162b920870de81b89f2
5 files changed