Remove access to the (P)urge user command from the (O)perator menu for sub-ops.

They can use the user editor to do this if they have a higher SL than the
poster.

src/sbbs3/readmsgs.cpp

@@ -939,9 +939,9 @@ int sbbs_t::scanposts(uint subnum, long mode, const char *find)
 					if(!(useron.misc&EXPERT))
 						menu("sysmscan");
 					bputs(text[OperatorPrompt]);
-					strcpy(str,"?CEHMPQUV");
+					strcpy(str,"?CEHMQUV");
 					if(SYSOP)
-						strcat(str,"S");
+						strcat(str,"SP");
 					switch(getkeys(str,0)) {
 						case '?':
 							if(useron.misc&EXPERT)