ios: Various reverts of FRE experiment for MICe / default browser promo.

This CL reverts:
"[iOS] M103 FRE Experiment Setup: MICe and Default Browser promo"
in commit 92c84ba596f585e52847a7bc363770356cd6b31f.
and
"[iOS] Renaming the feature to enable default browser promo"
in commit dc3b85226366409ecd761ad54f135c6a931d7256.
and
"[iOS] Turn on MICeAndDefaultBrowserPromo experiment on stable"
in commit 2e6bf3b01a83eb42490e59b09f0c91113de5e886.

Reason for revert: Lots of FirstRunTestCase and ForcedSigninTestCase:
   chrome/builders/ci/iphone-device/28799/overview
   chrome/builders/ci/ipad-device/28410/overview
   chrome/builders/ci/ipad-simulator/31988/overview

Change-Id: I36df96c4da3dabf50538c08bd2fb998242ac6ae6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3668370
Reviewed-by: Ginny Huang <ginnyhuang@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Owners-Override: Justin Cohen <justincohen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1007847}
NOKEYCHECK=True
GitOrigin-RevId: 273add97f71eaf12882f39b05bb7484fa49e652a
11 files changed