Remove the Core prefix from generated clients

[steveluscher]

Fixes #3.

[buffalojoec]

This looks good to me. It's a temporary thing for now, but we likely won't have a real solution to the underlying reason the program ID is different for a while.

For more info, see solana-program/loader-v4#10

TL/DR: The runtime will invoke loader v3 to invoke a BPF program, so if loader v3 itself is a BPF program, it can't also invoke a BPF program in the same way. The runtime needs to split this function out from the BPF Loader builtin, and we'll have to explore doing that before we can use the real program ID to test in here.