Do not use `free` with string buffer returned by `umkaAsm`

The Umka compiler has been switched to a garbage-collecting allocator. You no longer need to use `free` with the string buffer returned by `umkaAsm`. The buffer pointer stays valid until `umkaFree` is called. Using `free` causes a segmentation fault. Remove this line: https://github.com/tophat2d/tophat/blob/main/src/main.c#L156