Specify DEPS ninja path directly in build scripts instead of depot_tools/ninja wrapper

It's better to avoid calling DEPOT_TOOLS_PATH because ninja binaries in depot_tools will be removed soon.
Technically, it would work because depot_tools/ninja 'wrapper' can find the DEPS ninja path. But it's better to specify the ninja path directly instead of relying on the wrapper.

Bug: chromium:1340825
Change-Id: I992c12601e86be003acdb39ce6d29be817dc7522
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/286520
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Auto-Submit: Junji Watanabe <jwata@google.com>
Cr-Commit-Position: refs/heads/main@{#38815}
diff --git a/tools_webrtc/android/build_aar.py b/tools_webrtc/android/build_aar.py
index 42a902c..d910b39 100755
--- a/tools_webrtc/android/build_aar.py
+++ b/tools_webrtc/android/build_aar.py
@@ -121,7 +121,7 @@
 
 def _RunNinja(output_directory, args):
   cmd = [
-      os.path.join(find_depot_tools.DEPOT_TOOLS_PATH, 'ninja'), '-C',
+      os.path.join(SRC_DIR, 'third_party', 'ninja', 'ninja'), '-C',
       output_directory
   ]
   cmd.extend(args)