Revert "gclient: Add skip-git experiment."

This reverts commit 8672d51b79.

Reason for revert: crrev.com/c/5018522 has landed, so this is no longer required.

Original change's description:
> gclient: Add skip-git experiment.
>
> This experiment causes all dependencies of type 'git' to be skipped for
> all commands. This can be useful if you need to build Chromium in a
> working tree that is guaranteed to contain a consistent, pre-synced
> snapshot of the code that's managed by Git, but still need to install
> cipd dependencies and run the hooks to download the remaining
> dependencies.
>
> Bug: b/310485239
> Change-Id: Iee1e6a4d62b867b6d7235903817f927a9e806dc1
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5018571
> Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>
> Auto-Submit: Philipp Wollermann <philwo@chromium.org>
> Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>

Bug: b/310485239
Change-Id: If1fc93d493daa9515ddfb568aecf4374deb6ec03
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5035260
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Josip Sokcevic <sokcevic@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@chromium.org>

gclient.py

@@ -128,13 +128,6 @@ PREVIOUS_SYNC_COMMITS = 'GCLIENT_PREVIOUS_SYNC_COMMITS'
 
 NO_SYNC_EXPERIMENT = 'no-sync'
 
-# This experiment causes all dependencies of type 'git' to be skipped for all
-# commands. This can be useful if you need to build Chromium in a working
-# tree that is guaranteed to contain a consistent, pre-synced snapshot of the
-# code that's managed by Git, but still need to install cipd dependencies and
-# run the hooks to download the remaining dependencies.
-SKIP_GIT_EXPERIMENT = 'skip-git'
-
 PRECOMMIT_HOOK_VAR = 'GCLIENT_PRECOMMIT'
 
 
@@ -1112,10 +1105,6 @@ class Dependency(gclient_utils.WorkItem, DependencySettings):
         # working copy state, so skip the SCM status check.
         run_scm = command not in ('flatten', 'runhooks', 'recurse', 'validate',
                                   None)
-        # See the description of the experiment for the logic behind this.
-        if SKIP_GIT_EXPERIMENT in options.experiments and isinstance(
-                self, GitDependency):
-            run_scm = False
         file_list = [] if not options.nohooks else None
         revision_override = revision_overrides.pop(
             self.FuzzyMatchUrl(revision_overrides), None)