spirv-llvm-translator: small recipe cleanup

spirv-llvm-translator: small recipe cleanup

- There is no need for python3native, as this recipe doesn't depend on
  other python modules.

- Inherit lib_package so the llvm-spirv binary is in a separate package
  to the libLLVMSPIRVLib.so library.

- Remove obsolete CMake options that no longer appear to be required.

- Change CMAKE_SKIP_RPATH to CMAKE_SKIP_BUILD_RPATH as this stops the
  ELF editing on install without potentially removing any explicit
  RPATHs, and aligns with a change I've proposed for cmake.bbclass.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>