Tests fail to compile: error: use of undeclared identifier 'unlink'

```
/usr/ports/biology/fastani/work/FastANI-1.34/src/cgi/core_genome_identity.cpp:162:11: error: use of undeclared identifier 'unlink'
  162 |           unlink(visFileName.c_str());
      |           ^
1 error generated.
```