Do not trigger duplicated blink-rel bots

Some blink-rel bots have cq counter parts. When rebaselining, running
such bots will waste resources, and cause non-deterministic results
when rebaselining. The reason is that we will randomly pick one bot
when there are duplicate bots.

Removed linux-blink-optional-highdpi-rel from builders.json and
'--flag-specific' from rebaseline-cl. Highdpi flag-specific tests
are running inside linux-rel. And rebaseline-cl will automatically
fetch flag specific results as long as the builders are triggered.

Also fixed the port mismatch for mac-rel.

Bug: 1353054
Change-Id: I31925521166bc169d416c3b536124bf994c60f83
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3828509
Reviewed-by: Jonathan Lee <jonathanjlee@google.com>
Commit-Queue: Weizhong Xia <weizhong@google.com>
Reviewed-by: Preethi Mohan <preethim@google.com>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1036460}