Replace check_log_err with log_includes/log_excludes

The latter are more explicit and easier to understand at the call site.

Also removed the redundant crash checks via the log files.

maxscale-system-test/testconnections.h

@@ -451,15 +451,6 @@ public:
 
     int check_t1_table(int m, bool presence, char* db);
 
-    /**
-     * @brief CheckLogErr Reads error log and tried to search for given string
-     * @param err_msg Error message to search in the log
-     * @param expected TRUE if err_msg is expedted in the log, false if err_msg should NOT be in the log
-     * @return 0 if (err_msg is found AND expected is TRUE) OR (err_msg is NOT found in the log AND expected
-     * is false)
-     */
-    void check_log_err(int m, const char* err_msg, bool expected);
-
     /**
      * @brief Check whether logs match a pattern
      *