[llvm] Revert "[RISCV] Add cost model tests for llvm.vector.{insert,extract}… (PR #81913)

[Philip Reames via llvm-commits]

preames wrote:

Just to close the loop here, sorry for the breakage.  The error was definitely mine, I didn't rebase after the new tests were added.  Thank you to @topperc for reverting my change.  

https://github.com/llvm/llvm-project/pull/81913