Sync cleanup: Remove UserSelectableType::kWifiConfigurations

The "Wifi configurations" data type still exists, but after the "Split
Settings Sync" project (crbug.com/1013466), it's controlled via
UserSelectableOsType::kOsWifiConfigurations. The browser version of the
UserSelectableType was unused.

Bug: 1059309
Change-Id: Id86de212c01df39af6fce2ebd3bc68bcf5879159
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4616069


Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Commit-Queue: Marc Treib <treib@chromium.org>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Reviewed-by: Nohemi Fernandez <fernandex@chromium.org>
Reviewed-by: Jana Grill <janagrill@google.com>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1159580}