lint: clean up len-as-condition warnings

Rather than count iterables just to test equality to 0, use their
implicit truthiness instead.  Shouldn't be any functional changes.

BUG=chromium:980619
TEST=`cros lint` is clean w/pylint-1.7 again

Change-Id: I3ebf4f3dc51bed492caaa85d14b87239f61d3a6c
Reviewed-on: https://chromium-review.googlesource.com/1816121
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Will Bradley <wbbradley@chromium.org>
diff --git a/pre-upload.py b/pre-upload.py
index 77c4d99..9a19ac7 100755
--- a/pre-upload.py
+++ b/pre-upload.py
@@ -722,7 +722,7 @@
     # Construct regex
     name_re = r'\b(%s)\b' % '|'.join([re.escape(x) for x in name_list])
     matches = [x[0] for x in re.findall(name_re, commit_message, re.IGNORECASE)]
-    if len(matches):
+    if matches:
       # If there's a match, throw an error.
       error_msg = ('Changelist description contains the name of an'
                    ' %s: "%s".' % (name_type, '","'.join(matches)))
@@ -1916,7 +1916,7 @@
   if proj_dir is None:
     proj_dirs = _run_command(
         ['repo', 'forall', project_name, '-c', 'pwd']).split()
-    if len(proj_dirs) == 0:
+    if not proj_dirs:
       print('%s cannot be found.' % project_name, file=sys.stderr)
       print('Please specify a valid project.', file=sys.stderr)
       return True