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}

tools_webrtc/android/build_aar.py

@@ -121,7 +121,7 @@ def _RunGN(args):
 
 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)

tools_webrtc/ios/build_ios_libs.py

@@ -197,7 +197,7 @@ def BuildWebRTC(output_dir, target_environment, target_arch, flavor,
   logging.info('Building target: %s', gn_target_name)
 
   cmd = [
-      os.path.join(find_depot_tools.DEPOT_TOOLS_PATH, 'ninja'),
+      os.path.join(SRC_DIR, 'third_party', 'ninja', 'ninja'),
       '-C',
       output_dir,
       gn_target_name,

tools_webrtc/presubmit_checks_lib/build_helpers.py

@@ -69,7 +69,7 @@ def RunGnCheck(root_dir=None):
 def RunNinjaCommand(args, root_dir=None):
   """Runs ninja quietly. Any failure (e.g. clang not found) is
      silently discarded, since this is unlikely an error in submitted CL."""
-  command = [os.path.join(find_depot_tools.DEPOT_TOOLS_PATH, 'ninja')] + args
+  command = [os.path.join(SRC_DIR, 'third_party', 'ninja', 'ninja')] + args
   p = subprocess.Popen(command,
                        cwd=root_dir,
                        stdout=subprocess.PIPE,