JDK-8343430 removed the old trampoline call on RISC-V. And the new solution (reloc call) loads a target address from stub and do an indirect call.
This means the stub is always there for a NativeCall. So there's no need to check existence of the stub when doing `CallRelocation::fix_relocation_after_move`.
We can always return the stub address in `NativeCall::reloc_destination` and use that address in `NativeCall::reloc_set_destination`.
This helps simplify the code and saves one `MacroAssembler::target_addr_for_insn` call and one `trampoline_stub_Relocation::get_trampoline_for` call in these two functions respectively.