Change logging level for Scrubbed PYTHONPATH from env message + use fstrings

[asherf]

Problem

If PYTHONPATH is defined in the env, this message will show up every time pants start, which is somewhat noisy (and also probably useless)

Solution

Change log level of that message

Result

Cleaner output in pants runs.

[asherf]

@Eric-Arellano @stuhood this is somewhat opinionated, but I keep seeing this message when running pants, so at some point it is clutter. but I understand that there is a reason to have it in other use cases.
So feel free to close this PR of this change is not appropriate.

[stuhood]

I'm fine with this.

Thanks!

[Eric-Arellano]

Thank you! This has also bothered me for a long time.