hide Plain Egg mounts and remove them from totalMounts count - fixes https://github.com/HabitRPG/habitrpg/issues/3240

Requires https://github.com/HabitRPG/habitrpg-shared/pull/308 which adds a "noMount" flag to the Plain Eggs.

Any egg with noMount:true is not counted in the total number of possible mounts and does not have a space reserved for it on the Mounts page.