Revert "Improve PYTHONPATH checker" (#3249)

Reverts #3085

This broke mac builders.

b/299098707

cobalt/build/gn.py

@@ -22,7 +22,6 @@
 from pathlib import Path
 from typing import List
 
-from starboard.build.is_on_path import is_on_same_path
 from starboard.build.platforms import PLATFORMS
 
 _BUILD_TYPES = ['debug', 'devel', 'qa', 'gold']
@@ -52,8 +51,6 @@ def main(out_directory: str, platform: str, build_type: str,
 
 
 if __name__ == '__main__':
-  assert is_on_same_path(__file__), 'Current repo is not first on PYTHONPATH.'
-
   parser = argparse.ArgumentParser()
 
   builds_directory_group = parser.add_mutually_exclusive_group()

starboard/build/is_on_path.py

@@ -16,28 +16,17 @@
 
 import os
 
-SRC_ROOT = src_root_dir = os.path.abspath(
-    os.path.join(os.path.dirname(__file__), os.pardir, os.pardir))
 
-
-def is_on_same_path(file_path):
-  """
-  Checks if the passed file path is in the same repo as this file.
-
-  Args:
-    file_path: The path to the file that should be checked.
-
-  Returns:
-    True if file_path is a file in the same repo as this file, otherwise False.
-  """
-  return os.path.abspath(file_path).startswith(SRC_ROOT)
-
-
-if __name__ == '__main__':
+def main():
   try:
+    # Try to import this file and compare its path to the current file.
     import starboard.build.is_on_path  # pylint: disable=import-outside-toplevel
-    # Use imported function instead of calling directly to ensure imports are
-    # being made from the same repo as this file is in.
-    print(str(starboard.build.is_on_path.is_on_same_path(__file__)).lower())
+    this_file = os.path.realpath(__file__)
+    imported_file = os.path.realpath(starboard.build.is_on_path.__file__)
+    print(str(this_file == imported_file).lower())
   except ImportError:
     print('false')
+
+
+if __name__ == '__main__':
+  main()