pgsql: Make SyncRepWakeQueue to a static function

Make SyncRepWakeQueue to a static function

It is only used in src/backend/replication/syncrep.c.

Back-patch to all supported branches except 9.1 which declares the
function as static.

Branch
------
REL9_4_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/3740bb8347a946232ad281174398a825c1b40c73

Modified Files
--------------
src/backend/replication/syncrep.c |    3 ++-
src/include/replication/syncrep.h |    3 ---
2 files changed, 2 insertions(+), 4 deletions(-)