Avoid __file__ / PyOxidizer support

PyOxidizer breaks on pwntools as it doesnt provide `__file__` See indygreg/PyOxidizer#69 for more info about why, but the tl;dr version is `__file__` is an optional attribute and should not be relied upon.

Currently the startup looks like
```py
>>> import pwnlib
Traceback (most recent call last):
File "", line 1, in
File "pwnlib", line 43, in
File "importlib", line 127, in import_module
File "pwnlib.args", line 62, in
File "pwnlib.term", line 6, in
File "pwnlib.term.completer", line 7, in
File "pwnlib.term.readline", line 9, in
File "pwnlib.term.text", line 126, in
File "pwnlib.term.text", line 27, in __init__
NameError: name '__file__' is not defined
```

It looks like many of the cases of `__file__` being used here are optional, and could be omitted if not present.