Delete gcl, drover, and trychange

These tools are relatively standalone, and only ever worked for SVN.
Removing these is a good start to removing other SVN support code.

R=maruel@chromium.org
BUG=475321

Review-Url: https://codereview.chromium.org/2269413002
diff --git a/git_cl.py b/git_cl.py
index 5831b12..7dc9bac 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -1025,7 +1025,7 @@
   def GetCCList(self):
     """Return the users cc'd on this CL.
 
-    Return is a string suitable for passing to gcl with the --cc flag.
+    Return is a string suitable for passing to git cl with the --cc flag.
     """
     if self.cc is None:
       base_cc = settings.GetDefaultCCList()