Move PYTHONPATH to .profile

The .bashrc file isn't the correct place to set PYTHONPATH in the first
place.  Rather than simply move that hard-coded value to .profile,
though, I've deleted it entirely and am relying on a symlink in
`~/lib/python3/dist-packages` to achieve the same function, with
.profile adding that more generally useful path to the PYTHONPATH
variable.