[LINTER] Remove the lint-format-strings.sh script

Summary:
The python script is now called directly by a dedicated PHP linter.
This avoids the bash intermediate step and cuts the time by about 3x.

Depends on D2882

Test Plan:

arc lint --everything

Should return no error

Comment any of the false positive at the beginning of the
lint-format-strings.py file.

arc lint --everything

Ensure the false positive are catched by the linter.

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D2883