[iOS][macOS] Eliminate use of bitcode_strip

Our executables are no longer built with bitcode enabled and thus
`bitcode_strip -r SOURCE -o DEST` is just copying the file in question
to the output location.

Use of Bitcode was eliminated in Flutter in 2022. See linked issue for
details.

This is a reland of flutter#54240
which was reverted in flutter#54250

The the previous version was reverted because Python's `shutil.copyfile`
doesn't set the unix permissions of the source file on the destination
file. However, when overwriting an existing destination file, it
preserves any permissions on that file. One can imagine how this might
be problematic if you test the script by running before and after the
change with the same output directory. `shutil.copy2` attempts to
preserve source file metadata when writing the copy.

Issue: flutter/flutter#107884

sky/tools/create_full_ios_framework.py

@@ -243,7 +243,7 @@ def _generate_gen_snapshot(gen_snapshot_path, destination):
     print('Cannot find gen_snapshot at %s' % gen_snapshot_path)
     sys.exit(1)
 
-  subprocess.check_call(['xcrun', 'bitcode_strip', '-r', gen_snapshot_path, '-o', destination])
+  shutil.copy2(gen_snapshot_path, destination)
 
 
 if __name__ == '__main__':

sky/tools/create_macos_gen_snapshots.py

@@ -5,6 +5,7 @@
 # found in the LICENSE file.
 
 import argparse
+import shutil
 import subprocess
 import sys
 import os
@@ -69,7 +70,7 @@ def generate_gen_snapshot(gen_snapshot_path, destination):
     print('Cannot find gen_snapshot at %s' % gen_snapshot_path)
     sys.exit(1)
 
-  subprocess.check_call(['xcrun', 'bitcode_strip', '-r', gen_snapshot_path, '-o', destination])
+  shutil.copy2(gen_snapshot_path, destination)
 
 
 if __name__ == '__main__':