Fix the following Nix/Home Manager evaluation warnings except for the gc/nh conflict warning:

- `evaluation warning: 'system' has been renamed to/replaced by 'stdenv.hostPlatform.system'`
- `evaluation warning: m3tam3re profile: programs.ssh.matchBlocks defined in /nix/store/...-users/m3tam3re/identities/private.nix is deprecated. Use programs.ssh.settings.`

Do not fix or change the warning:

- `evaluation warning: programs.nh.clean.enable and nix.gc.automatic are both enabled. Please use one or the other to avoid conflict.`

The private identity source file is in `/home/m3tam3re/p/NIX/m3ta-home/users/m3tam3re/identities/private.nix`.