chromite_wrapper: modernize a bit

This file hasn't been updated in over 6 years.  The backwards compat
logic in here dates back to pre-R20 releases, and the only boards we
released that long ago are EOL now.  So scrub all the unused code to
simplify it.

While we're here, fix a few style issues, and update the docs.

Bug: 997354
Test: `cros help` still works
Change-Id: Id226cd73f045972b88e7bc5926a415f567d1e41c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1875488
Reviewed-by: Mike Nichols <mikenichols@chromium.org>
Reviewed-by: Alex Klein <saklein@chromium.org>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>

support/chromite_wrapper

@@ -10,24 +10,11 @@ to find the path for chromite, and hands off to the right tool via exec if
 possible.
 
 It is intended to used strictly outside of the chroot.
-
-If you're looking at a copy and want to know where the original looks at, look
-here:
-  http://git.chromium.org/gitweb/?p=chromite.git;a=blob;f=bin/chromite
-
-Since this script is _copied_, it should remain small and not use internal libs.
-
 """
 
-import errno
 import os
 import sys
 
-# Due to historical reasons, and the fact depot_tools ToT is used by older
-# factory branches (lacking chromite script cleanups), note we have to
-# fallback to some odd import locations.  This is the only reason for the
-# fallback code- any/all new scripts symlinked to this script *must* exist
-# in chromite/bin/ .
 
 def _FindChromite(path):
   """Find the chromite dir in a repo, gclient, or submodule checkout."""
@@ -50,12 +37,11 @@ def _FindChromite(path):
 
 
 def _MissingErrorOut(target):
-  sys.stderr.write(
-"""ERROR: Couldn't find the chromite tool %s.
+  sys.stderr.write("""ERROR: Couldn't find the chromite tool %s.
 
 Please change to a directory inside your Chromium OS source tree
 and retry.  If you need to setup a Chromium OS source tree, see
-  http://www.chromium.org/chromium-os/developer-guide
+  https://chromium.googlesource.com/chromiumos/docs/+/HEAD/developer_guide.md
 """ % target)
   return 127
 
@@ -67,30 +53,8 @@ def main():
     return _MissingErrorOut(target)
 
   path = os.path.join(chromite_dir, 'bin', target)
-  try:
   os.execv(path, [path] + sys.argv[1:])
-  except EnvironmentError as e:
-    if e.errno not in (errno.ENOENT, errno.EPERM):
-      raise
-
-  # Reaching here means it's either a bad target, or we're working against
-  # an old (pre 6be2efcf5bb575b03862113eec097c44d8d7f93e) revision of
-  # chromite.  Fallback to trying to import it; this code works at least as
-  # far back as branch 0.11.241.B; likely further.
 
-  if target == 'cbuildbot':
-    target = 'chromite.buildbot.cbuildbot'
-  else:
-    target = 'chromite.bin.%s' % (target,)
-
-  # Adjust the path importation so we can import our our target.
-  sys.path.insert(0, os.path.dirname(chromite_dir))
-
-  try:
-    module = __import__(target, fromlist=['main'])
-  except ImportError:
-    return _MissingErrorOut(target)
-  return module.main()
 
 if __name__ == '__main__':
   sys.exit(main())