pgsql: Remove FileUnlink(), which wasn't being used anywhere and

Log Message:
-----------
Remove FileUnlink(), which wasn't being used anywhere and interacted poorly
with the recent patch to log temp file sizes at removal time. Doesn't seem
worth fixing since it's unused.
In passing, make a few elog messages conform to the message style guide.

Modified Files:
--------------
pgsql/src/backend/storage/file:
fd.c (r1.139 -> r1.140)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/file/fd.c.diff?r1=1.139&r2=1.140)
pgsql/src/include/storage:
fd.h (r1.59 -> r1.60)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/storage/fd.h.diff?r1=1.59&r2=1.60)