Update HINT for pre-existing shared memory block.

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

src/backend/utils/init/miscinit.c

@@ -1066,14 +1066,10 @@ CreateLockFile(const char *filename, bool amPostmaster,
 				if (PGSharedMemoryIsInUse(id1, id2))
 					ereport(FATAL,
 							(errcode(ERRCODE_LOCK_FILE_EXISTS),
-							 errmsg("pre-existing shared memory block "
-									"(key %lu, ID %lu) is still in use",
+							 errmsg("pre-existing shared memory block (key %lu, ID %lu) is still in use",
 									id1, id2),
-							 errhint("If you're sure there are no old "
-									 "server processes still running, remove "
-									 "the shared memory block "
-									 "or just delete the file \"%s\".",
-									 filename)));
+							 errhint("Terminate any old server processes associated with data directory \"%s\".",
+									 refName)));
 			}
 		}