Revert "res_rtp_asterisk.c: Set Mark on rtp when timestamp skew is too big"

This reverts commit f30ad96b3f.

The original change was not RFC compliant and caused issues because it
set the RTP marker bit in cases when it shouldn't be set. See the
linked issue #1135 for a detailed explanation.

Fixes: #1135.
(cherry picked from commit 5565d00eb4)

res/res_rtp_asterisk.c

@@ -5266,11 +5266,6 @@ static int rtp_raw_write(struct ast_rtp_instance *instance, struct ast_frame *fr
 	}
 
 	if (ast_test_flag(frame, AST_FRFLAG_HAS_TIMING_INFO)) {
-		if (abs(frame->ts * rate - (int)rtp->lastts) > MAX_TIMESTAMP_SKEW) {
-			ast_verbose("(%p) RTP audio difference is %d set mark\n",
-				instance, abs(frame->ts * rate - (int)rtp->lastts));
-			mark = 1;
-		}
 		rtp->lastts = frame->ts * rate;
 	}