[Build] Fix --android-deps-dir parameter in android_deps/fetch_all.py

This CL removes the trailing slash - if there is one - from the
--android-deps-dir command line parameter to
//third_party/android_deps/fetch_all.py

BUG=1132330

Change-Id: I8800cdc8ebc38150a47a52333646e86b24dd9b2a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437021Reviewed-by: Sam Maier <smaier@chromium.org>
Commit-Queue: Peter Kotwicz <pkotwicz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811816}

third_party/android_deps/fetch_all.py

@@ -409,6 +409,9 @@ def main():
         format='%(levelname).1s %(relativeCreated)6d %(message)s')
     debug = args.verbose_count >= 2
 
+    if args.android_deps_dir.endswith("/"):
+        args.android_deps_dir = args.android_deps_dir[:-1]
+
     abs_android_deps_dir = os.path.normpath(
         os.path.join(_CHROMIUM_SRC, args.android_deps_dir))