[static runtime] Shortcut resize_({0})
Summary:
We do a lot of resize_({0}) to force `out` operators to properly
resize their results, and `resize_` does a fair bit of extraneous work
(e.g. trip through dispatch, checks for memory_format and named tensors, etc.).
If we strip it down to the bare minimum it's just setting the sizes to 0, so
lets do that directly.
Test Plan:
Perf results suggest maybe a 1% win:
```
batch 20: P163138256 (large win, 1.7%, mostly in fb_fc_out)
batch 1: P163139591 (smaller win, 0.88%, mostly in resize_)
```
Reviewed By: swolchok
Differential Revision: D25932595
fbshipit-source-id: d306a0a15c0e1be12fde4a7f149e3ed35665e3c0
