cppcheck: remove knownConditionTrueFalse suppression

[fenugrec]

cppcheck-2.6 can't follow the sequence

	msg = msg->next;
	if (msg == NULL) {
		return CMD_OK;
	}

	msg = msg->next;
	if (msg == NULL) {
		return CMD_OK;
	}

in scantool_850.c:1232 .

see https://sourceforge.net/p/cppcheck/discussion/general/thread/7ff3948cbc/ and its ticket (fixed and included in cppcheck-2.7) https://trac.cppcheck.net/ticket/10649

When cppcheck 2.7 eventually lands in more distros, we can remove the suppression.