移除 FreeSql.DbContext，成为独立项目

FreeSql.DbContext/DbContext/DbContextOptionsBuilder.cs

@@ -1,18 +0,0 @@
-using Microsoft.Extensions.Caching.Distributed;
-using Microsoft.Extensions.Logging;
-using System;
-using System.Collections.Generic;
-using System.Data.Common;
-using System.Text;
-
-namespace FreeSql {
-	public class DbContextOptionsBuilder {
-
-		internal IFreeSql _fsql;
-
-		public DbContextOptionsBuilder UseFreeSql(IFreeSql orm) {
-			_fsql = orm;
-			return this;
-		}
-	}
-}