Revert "Use pylint 2.7 for depot_tools"

This reverts commit 22bf605bb63f8ff01aa7c1a2841718e3489b43d6.

Reason for revert: breaks gclient sync

Original change's description:
> Use pylint 2.7 for depot_tools
>
> This includes a few fixes for specific errors, and disables several new
> warnings introduced in this version, in order to allow for an incremental migration.
>
> Bug:1262286
> Change-Id: Ie97d686748c9c952e87718a65f401c5f6f80a5c9
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3400616
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Aravind Vasudevan <aravindvasudev@google.com>

Bug: 1262286
Change-Id: Ieb946073c7886c7bf056ce843a5a48e82becf7a5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3413672
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
diff --git a/fetch.py b/fetch.py
index 74b2298..c4b605c 100755
--- a/fetch.py
+++ b/fetch.py
@@ -56,6 +56,7 @@
 
   def exists(self):
     """Check does this checkout already exist on desired location"""
+    pass
 
   def init(self):
     pass
@@ -66,18 +67,18 @@
       return ''
     if return_stdout:
       return subprocess.check_output(cmd, **kwargs).decode()
-
-    try:
-      subprocess.check_call(cmd, **kwargs)
-    except subprocess.CalledProcessError as e:
-      # If the subprocess failed, it likely emitted its own distress message
-      # already - don't scroll that message off the screen with a stack trace
-      # from this program as well. Emit a terse message and bail out here;
-      # otherwise a later step will try doing more work and may hide the
-      # subprocess message.
-      print('Subprocess failed with return code %d.' % e.returncode)
-      sys.exit(e.returncode)
-    return ''
+    else:
+      try:
+        subprocess.check_call(cmd, **kwargs)
+      except subprocess.CalledProcessError as e:
+        # If the subprocess failed, it likely emitted its own distress message
+        # already - don't scroll that message off the screen with a stack trace
+        # from this program as well. Emit a terse message and bail out here;
+        # otherwise a later step will try doing more work and may hide the
+        # subprocess message.
+        print('Subprocess failed with return code %d.' % e.returncode)
+        sys.exit(e.returncode)
+      return ''
 
 
 class GclientCheckout(Checkout):