[locales] Remove locales reference

This CL removes the locales variable from build/config/locales.gni.

All references to locales have been changed to platform_pak_locales.
If this CL breaks a downstream build please rename the locales variable
there.

Bug: 1293908
Change-Id: Ia722e7856510abf96e7fadcbf2a0f73022bc8abe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3445327


Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Commit-Queue: Trevor Perrier <perrier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#970710}