Revert "[Quant][fx][bc-breaking] Make convert.py smaller (#90189)"
This reverts commit 824641b083860df4d7ffef06a798ea2702bc4bde.
Reverted https://github.com/pytorch/pytorch/pull/90189 on behalf of https://github.com/seemethere due to Fails internal tests due to potential circular import, see https://www.internalfb.com/diff/D41817429?dst_version_fbid=1453307181865235&transaction_fbid=899728221278938
