One should almost always terminate an old process, not use a manual
removal tool like ipcrm.  Removal of the ipcclean script eleven years
ago (39627b1a) and its non-replacement
corroborate that manual shm removal is now a niche goal.  Back-patch to
9.4 (all supported versions).

Reviewed by Daniel Gustafsson and Kyotaro HORIGUCHI.

Discussion: https://postgr.es/m/20180812064815.GB2301738@rfd.leadboat.com