Remove SpecOptionPartialEq
With the recent LLVM bump, the specialization for Option::partial_eq on types with niches is no longer necessary. I kept the manual implementation as it still gives us better codegen than the derive (will look at this seperately).
Also implemented PartialOrd/Ord by hand as it _somewhat_ improves codegen for #49892: https://godbolt.org/z/vx5Y6oW4Y
cdb683f6e4