patman: Drop an incorrect comment about git am

Patman does not do this anymore, as of this commit:

   7428dc14b0f ("patman: Remove the -a option")

Drop the comment.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
diff --git a/tools/patman/control.py b/tools/patman/control.py
index d1bcea0..916ddf8 100644
--- a/tools/patman/control.py
+++ b/tools/patman/control.py
@@ -85,7 +85,7 @@
     # Do a few checks on the series
     series.DoChecks()
 
-    # Check the patches, and run them through 'git am' just to be sure
+    # Check the patches
     if run_checkpatch:
         ok = checkpatch.check_patches(verbose, patch_files, use_tree)
     else: