Remove __getattribute__ on autograd.Function (#122033)
Improves `benchmarks/dynamo/microbenchmarks/overheads.py` from 38.7us to
34.3us.
See #122029
Pull Request resolved: https://github.com/pytorch/pytorch/pull/122033
Approved by: https://github.com/zou3519, https://github.com/soulitzer
ghstack dependencies: #122032
