[libc] Remove the 'rpc_reset' routine from the RPC implementation (#66700)

Summary:
This patch removes the `rpc_reset` function. This was previously used to
initialize the RPC client on the device by setting up the pointers to
communicate with the server. The purpose of this was to make it easier
to initialize the device for testing. However, this prevented us from
enforcing an invariant that the buffers are all read-only from the
client side.

The expected way to initialize the server is now to copy it from the
host runtime. This will allow us to maintain that the RPC client is in
the constant address space on the GPU, potentially through inference,
and improving caching behaviour.