pgsql: process startup: Remove bootstrap / checker modes from AuxProcTy

process startup: Remove bootstrap / checker modes from AuxProcType.

Neither is actually initialized as an auxiliary process, so it does not really
make sense to reserve a PGPROC etc for them.

This keeps checker mode implemented by exiting partway through bootstrap
mode. That might be worth changing at some point, perhaps if we ever extend
checker mode to be a more general tool.

Author: Andres Freund 
Reviewed-By: Kyotaro Horiguchi 
Reviewed-By: Robert Haas 
Discussion: https://postgr.es/m/20210802164124.ufo5buo4apl6yuvs@alap3.anarazel.de

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/f8dd4ecb0b7fc3420e199021375e622815cd326f

Modified Files
--------------
src/backend/bootstrap/bootstrap.c   | 29 +++++++++++------------------
src/backend/main/main.c             |  8 +++++---
src/backend/postmaster/auxprocess.c |  5 -----
src/bin/initdb/initdb.c             |  6 +++---
src/include/bootstrap/bootstrap.h   |  2 +-
src/include/miscadmin.h             |  5 +----
6 files changed, 21 insertions(+), 34 deletions(-)