Simplify build files now that arm_use_neon is always true

...and arm_version is always >= 7.

This is true after
https://chromium-review.googlesource.com/c/chromium/src/+/7262201

No intended behavior change.

Bug: 469092869
Change-Id: I65b5a3fb37caa464bf88c4539bdc8f578075bb25
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7265333
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Reviewed-by: James Zern <jzern@google.com>
Reviewed-by: Felicia Lim <flim@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Sam Zackrisson <saza@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1560104}
NOKEYCHECK=True
GitOrigin-RevId: 2611e591a90fc90edcfc2e2bb52478b92f7ab7c7