[pytorch][size] remove unused SparseCPUType from mobile build (#33517)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33517
I don't think any mobile model uses SparseCPU backend yet so we can skip
generating dispatch code for this backend type.
This will help reduce mobile code size with dynamic dispatch turned on,
roughly ~100K for uncompressed iOS: D19616007 +413K v.s. D19616016 +319K.
It probably doesn't affect much static dispatch build size as the unused
static dispatch methods will be stripped by linker in the end.
ghstack-source-id: 98615810
Test Plan: - CI & BuildSizeBot
Reviewed By: linbinyu
Differential Revision: D19978633
fbshipit-source-id: 27bf6ada2ba98482084cf23724cf400b538b0a03
