Remove unnecessary paranoid check.

The OP_COUNT_IN operation does not need the paranoid check on r1 as it is the
lower bound of the range, and thus a constant and not a pointer somewhere. It
should, instead, be checking r3.

Fixes #1721 (the first half of it).

libyara/exec.c

@@ -1406,10 +1406,6 @@ int yr_execute_code(YR_SCAN_CONTEXT* context)
       ensure_defined(r1);
       ensure_defined(r2);
 
-#if YR_PARANOID_EXEC
-      ensure_within_rules_arena(r1.p);
-#endif
-
       match = context->matches[r3.s->idx].head;
       r4.i = 0;