Remove force-free of "leaked" memory in mem_display_blocks

mem_display_blocks runs before global destructors, so it reports as
leaked any memory which is managed by a global scope object with a
destructor.  If mem_display_blocks calls mem_free, and the destructor
later calls mem_free, a double-free results, and usually leads to a
crash.  Even if the memory were actually leaked, freeing it does not
help because the program will exit soon anyway.

Reported-by: zico <https://github.com/dxx-rebirth/dxx-rebirth/issues/85>

similar/mem/mem.cpp

@@ -320,7 +320,6 @@ void mem_display_blocks()
 				con_printf(CON_CRITICAL, "\nMEM_LEAKAGE: Memory block has not been freed." );
 				PrintInfo( i );
 			}
-			mem_free( (void *)MallocBase[i] );
 		}
 	}