Add the method file.remove and a test of its functionality.

In addition to the ability to remove a file by specifying its name, the
ability to remove a file from the file record provided is useful functionality.
This commit adds two methods: a version that generates an error if
something goes wrong, and a version that merely returns said error.
If either method completed successfully, the file record will no longer store
a valid file pointer.
Under the covers, these methods call out to removeFile with their path name.

This commit also adds a test that this works.