libmtp: move from chromium/ to src/chromium/

We've been moving the other chromium repos under this tree.

BUG=None
TEST=CQ passes

Change-Id: I783f09722e40923e02ddbd55b2f377ecd81c668f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/manifest/+/1761354Reviewed-by: Michael Mortensen <mmortensen@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>

full.xml

@@ -442,7 +442,7 @@ Your sources have been sync'd successfully.
            name="chromium/llvm-project/cfe/tools/clang-format"
            remote="chromium"
            groups="minilayout,buildtools,labtools" />
-  <project path="chromium/src/third_party/libmtp"
+  <project path="src/chromium/src/third_party/libmtp"
            name="chromium/deps/libmtp"
            remote="chromium" />
   <project path="src/chromium/src/third_party/Python-Markdown"