Remove duplicate module in the wrong place

[bwatters-r7]

While checking out #12391, I discovered we have both a modules/post/windows/manage/payload_inject and a modules/exploit/windows/local/payload_inject. Both appear to perform the same function with the same underlying calls to allocate memory to the remote process, write to it, then launch a thread. In the case of the post version, there's a lot more overhead associated with the payload listener, as it is not directly supported.
If there's something in the metasploit mythology that explains this, we can close this, but otherwise, let's delete the post module?

[busterb]

Added aadfb84

msf5 auxiliary(admin/juniper/juniper_config) > use post/windows/manage/payload_inject

[!] *             The module post/windows/manage/payload_inject has been moved!              *
[!] *                 You are now using exploit/windows/local/payload_inject                 *
msf5 exploit(post/windows/manage/payload_inject) >