reset_shared just invokes CreateSharedMemoryAndSemaphores, so let's
get rid of it and invoke that directly. This removes a confusing
seeming-inconsistency between the postmaster's startup sequence
and the startup sequence used in standalone mode.
Nathan Bossart, reviewed by Pavel Borisov
Discussion: https://postgr.es/m/20220329221702.GA559657@nathanxps13