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.