Stop searching-for and deleting INTRSBBS.DAT before running any external.

This is an artifact from SBBS v2 for DOS:
The file would contain the address of a shadow of the modem status register
(written by execdos.exe) for dropped-carrier detection in xsdk doors (or the
"dcdwatch" utility) while the BBS was "shrunk" out of memory to execute the
external program with maximal available memory.

src/sbbs3/xtrn_sec.cpp

@@ -1723,9 +1723,6 @@ bool sbbs_t::exec_xtrn(uint xtrnnum)
 		logfile_fp=NULL;
 	}
 
-	sprintf(str,"%sINTRSBBS.DAT"
-			,cfg.xtrn[xtrnnum]->path[0] ? cfg.xtrn[xtrnnum]->path : cfg.node_dir);
-	removecase(str);
 	sprintf(str,"%shangup.now",cfg.node_dir);
 	removecase(str);
 	sprintf(str,"%sfile/%04u.dwn",cfg.data_dir,useron.number);