More obsolete functionality removed.

The log manager possibility for explicitly specifying the names
of the log files has never been used. In the name of simplicity
that functionality is removed.

log_manager/log_manager.h

@@ -174,8 +174,6 @@ int skygw_log_get_augmentation();
 
 EXTERN_C_BLOCK_END
 
-const char* get_err_prefix_default(void);
-const char* get_err_suffix_default(void);
 const char* get_logpath_default(void);
 
 /**