pgsql: Finish up XLOG_HINT renaming

Finish up XLOG_HINT renaming

Commit b8fd1a09f3 renamed XLOG_HINT to XLOG_FPI, but neglected two
places.

Backpatch to 9.3, like that commit.

Branch
------
REL9_5_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/6fce92a7d7090fe02c39837908b4feb55806b3ee

Modified Files
--------------
src/backend/access/transam/README   | 2 +-
src/backend/storage/buffer/bufmgr.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)