[PJRT:CPU] Replace references to pjrt/tfrt_cpu_pjrt_client with pjrt/cpu/cpu_client.h.
[PJRT:CPU] Replace references to pjrt/tfrt_cpu_pjrt_client with pjrt/cpu/cpu_client.h.

The two are aliases and the former is a forwarding header pointing to the latter.

Cleanup only, no functional changes.

Reverts 5bbc00214f106863808539104be9fdc6e01af02d
