[ios] Delete UnifiedConsentCoordinator

Was unused.
- Some of the images in /unified_consent/resources/ are still used by
  /views/identity_button_control.mm [1] and thus are moved to the same
 directory.
- /unified_consent/identity_chooser/ is left as is for now, it should
  be moved one directory up in future CLs.

[1] https://source.chromium.org/chromium/chromium/src/+/main:ios/chrome/browser/ui/authentication/views/identity_button_control.mm;l=149-157;drc=c6d9e7de636cc5710744c3330d1063ab1792ce3d

Bug: 330333634
Change-Id: I16575df734d35ca76d806c39859125da2fa6e2a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5398116


Reviewed-by: Menghan Yang <myuu@google.com>
Commit-Queue: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/main@{#1278952}