Remove MiraclePtr-related options from clang plugin

These options are no longer used in the clang plugin, since MiraclePtr
enforcement was split into a separate plugin in crrev.com/c/5529293.

Bug: 331840473
Change-Id: I9f72efa4dc2f7ea1a84f756ab98791fd001b0cb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7841301
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1630888}
NOKEYCHECK=True
GitOrigin-RevId: 81a6018d6854b68d1184fae0004987df46977e96