pgsql: Remove am_syslogger global variable

Remove am_syslogger global variable

Use the new MyBackendType instead. More similar changes for other "am
something" variables are possible. This one was just particularly
simple.

Reviewed-by: Julien Rouhaud <rjuju123(at)gmail(dot)com>
Reviewed-by: Kuntal Ghosh <kuntalghosh(dot)2007(at)gmail(dot)com>
Reviewed-by: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/c65e5196-4f04-4ead-9353-6088c19615a3(at)2ndquadrant(dot)com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d90bd24391fdde2b73906e16052821c9e3c1ce82

Modified Files
--------------
src/backend/postmaster/syslogger.c | 9 +--------
src/backend/utils/error/elog.c | 8 ++++----
src/include/postmaster/syslogger.h | 2 --
3 files changed, 5 insertions(+), 14 deletions(-)