fold the last round of sql manager changes back into the core and use it for the central db and simplify the algorithm

src/include/private/switch_core_pvt.h

@@ -256,8 +256,6 @@ struct switch_runtime {
 	switch_profile_timer_t *profile_timer;
 	double profile_time;
 	double min_idle_time;
-	int sql_buffer_len;
-	int max_sql_buffer_len;
 	switch_dbtype_t odbc_dbtype;
 	char hostname[256];
 	char *switchname;