Don't Block Removing File on Being Able to Read It

Don't Block Removing File on Being Able to Read It

`open()`'s mode bits are only applied to files that are created by the call.
If the output file already exists, but is not readable, the `fopen()` would
fail, preventing us from removing it, which would mean that the file would
not end up with the correct permission bits.

It's not clear to me why the `fopen()` is there at all. `UTIL_isRegularFile()`
should be sufficient, AFAICT.