Reland "[AX Mac] Pretty print AXCustomContent from ax_dump_tree external macOS dumps"

This reverts commit 038e0a2893512d9a5fb2a5321afd452912565ef0.

Reason for revert: The original patch revealed a bug that existed in macOS 11, specifically, that the AX API attribute AXCustomContent was not yet supported.

This patch turns off the tests which test AXCustomContent for macOS 11.

Original change's description:
> Revert "[AX Mac] Pretty print AXCustomContent from ax_dump_tree external macOS dumps"
>
> This reverts commit 95ea439983ec79832f6f2e12c924f2a54928cd3c.
>
> Reason for revert: Suspected of causing test failures:
> https://ci.chromium.org/ui/p/chromium/builders/ci/mac11-arm64-rel-tests/47888/overview
>
> Original change's description:
> > [AX Mac] Pretty print AXCustomContent from ax_dump_tree external macOS dumps
> >
> > Bug: 363275809
> > Change-Id: Id65789495fa28f2599ccee9ca9602842263d7ada
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5926150
> > Reviewed-by: Jayson Adams <shrike@chromium.org>
> > Commit-Queue: Valerie Young <spectranaut@igalia.com>
> > Reviewed-by: David Tseng <dtseng@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#1375503}
>
> Bug: 363275809
> Change-Id: I2f380d3ca8dbf228ab1f9b47dc9a9d045e5adf32
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5974676
> Owners-Override: Takumi Fujimoto <takumif@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Auto-Submit: Takumi Fujimoto <takumif@chromium.org>
> Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1375578}

Bug: 363275809
Cq-Include-Trybots: luci.chromium.try:mac11.0-blink-rel,mac11.0.arm64-blink-rel
Change-Id: I27e711cd5a2a44b35c190f66f137b17cac213e22
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5976533
Commit-Queue: Valerie Young <spectranaut@igalia.com>
Reviewed-by: Jayson Adams <shrike@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1378035}