rust: Do not modify rpaths in llvm-config

rust: Do not modify rpaths in llvm-config

No need to edit rpaths in llvm-config, this is not
needed anymore because the llvm-config used is from
standard install inside sysroot unlike when rust-llvm
was used, where it was installed into its own location
to avoid conflicts with llvm-config coming from llvm/clang

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Cc: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>