pgsql: Remove silent_mode. You get the same functionality with "pg_ctl

Remove silent_mode. You get the same functionality with "pg_ctl -l
postmaster.log", or nohup.

There was a small issue with LINUX_OOM_ADJ and silent_mode, namely that with
silent_mode the postmaster process incorrectly used the OOM settings meant
for backend processes. We certainly could've fixed that directly, but since
silent_mode was redundant anyway, we might as well just remove it.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/f7ea6beaf4ca02b8e6dc576255e35a5b86035cb9

Modified Files
--------------
doc/src/sgml/config.sgml | 30 -------
src/backend/postmaster/postmaster.c | 113 +------------------------
src/backend/utils/misc/guc.c | 10 --
src/backend/utils/misc/postgresql.conf.sample | 5 -
4 files changed, 1 insertions(+), 157 deletions(-)