Enhance disabled convar

[sarahsturgeon]

This PR fixes a few cases where players' prop2mesh_disable convar is ignored.

Will stay in Draft status until I can test it properly, but I'm happy to receive reviews in the meantime.

[shadowscion]

Can you elaborate? The entire thing was probably unnecessary to begin with but the way I envisioned the two convars working together was "server convar has to be true for client convar to do anything". It was supposed to be a middle ground between build servers and competitive servers where disabling might give one a visual advantage. I wouldn't be opposed to removing the server setting altogether if it's causing issues.

[sarahsturgeon]

On our build server, people are frustrated that they disable P2M but still receive and process mesh data. The system you implemented allows server owners the ability determine if a player can actually turn off P2M - that works fine, but these two net.Broadcast calls don't respect the clientside convar and sends the data to all clients regardless of if they have P2M turned off