[llvm] [RISCV] Remove setJumpIsExpensive(). (PR #74647)

[Wang Pengcheng via llvm-commits]

wangpc-pp wrote:

How about adding it to `RISCVSubtarget` and changing it to something like:
```c
setJumpIsExpensive(Subtarget.isJumpExpensive())
```
So that processors can tune it.

https://github.com/llvm/llvm-project/pull/74647