[discord-rpc] Remove unneeded dependency

[Thomas1664]

• [x] Changes comply with the maintainer guide.
• [x] SHA512s are updated for each updated download.
• [x] The "supports" clause reflects platforms that may be fixed by this new version.
• [x] Any fixed CI baseline entries are removed from that file.
• [x] Any patches that are no longer applied are deleted from the port's directory.
• [x] The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• [x] Only one version is added to each modified port's versions file.