Update on "[reland][quant][graphmode][fx] Merge all quantization mode (…

…#45292)"

Summary:
This PR merges all quantization mode and will only expose the following top level functions:
```
prepare_fx
prepare_qat_fx
convert_fx
```

Test Plan: Imported from OSS

Reviewed By: vkuzo

Differential Revision: [D24053439](https://our.internmc.facebook.com/intern/diff/D24053439)

[ghstack-poisoned]

test/quantization/test_quantize_fx.py

@@ -14,7 +14,6 @@
 # graph mode quantization based on fx
 from torch.quantization import (
     QuantType,
-    fuse_fx,
     prepare_fx,
     convert_fx,
     prepare_qat_fx,