[llvm] [RISCV] Xqcilb: remove RISCVMCExpr::VK_QC_E_JUMP_PLT and drop `@plt` parsing (PR #135507)

[Sam Elliott via llvm-commits]

https://github.com/lenary approved this pull request.

LGTM. I am considering renaming the relocation but I will do it in a follow-up if I do because it needs coordinating over this and the ELD repo. 

https://github.com/llvm/llvm-project/pull/135507