Add admin-only map checks; remove compiled plugins

Introduce MMC_IsMapAdminOnly in multimode/utils.inc to detect admin-only maps from gamemode data. Update admin menu to label admin-only maps and prevent non-admin interactions: core.sp now skips admin-only maps for regular votes, random selection, and vote preparation unless an admin vote/current vote admin; nominations.sp prevents nominating admin-only maps. Also remove numerous compiled .smx plugin binaries from addons/sourcemod/plugins.

Author: TheDGB