Convert Python code from "%-formatted" and .format(...) strings into f-strings
Remove existing conversion script that only handles %-formatted strings.
TODO:Performance impact:
Before:
```
$ time arc lint --everything
real 2m15,395s
user 9m59,264s
sys 1m8,720s
```
After:
```
- wait for a new flynt release to have the stdin/stdout features$ time arc lint --everything
- check the next release version is indeed 0.78
- if the next release includes https://github.com/ikamensh/flynt/pull/164, then we don't need the stdin business: remove the overloading of buildfutures
- check if the next release fixes the extra newline added to stdout (I mentionned it to the devs on github)real 2m14,881s
user 10m6,171s
sys 1m8,421s
```