Remove @SystemApi from some constants for R.

These were exposed for telephony mainline. Will be revisited in S.

Test: basic sanity
Bug: 148171847
Bug: 148171388
Merged-in: Ibdcac557cf35e723f09a7b7a2e59c7deae1fc94e
Change-Id: Ibdcac557cf35e723f09a7b7a2e59c7deae1fc94e
(cherry picked from commit c55b0155)