Fix duplicate lock IDs & simplify lock ID maintenance.

* Eliminate the possibility of multiple lock IDs having the same
  value (CRYPTO_LOCK_FIPS2 and CRYPTO_LOCK_OBJ were both 40 prior to
  this commit).
* Remove unused lock IDs.
* Automatically guarantee that lock IDs and lock names stay in sync.

Change-Id: If20e462db1285fa891595a7e52404ad011ff16f6
Reviewed-on: https://boringssl-review.googlesource.com/3923
Reviewed-by: Adam Langley <agl@google.com>