[llvm] [RISCV] Remove machine-csr-names-invalid.s. NFC (PR #109595)

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> > > > Maybe we should rename `rv32-only-csr-names.s ` to a suitable name?
> > > 
> > > 
> > > Do you have a suggestion?
> > 
> > 
> > Maybe `machine-csr-names-invalid.s`? 😂
> 
> It only tests CSR names that are valid for rv32 and invalid for rv64. So rv64-machine-csr-names-invalid.s?

Never mind. Then I think its original name is OK as well. 😂

https://github.com/llvm/llvm-project/pull/109595