[tests] remove flake8-string-format test

flake8-string-format package is not maintained for 4 years; therefore
remove it. Valuable tests are already made by pyflake within flake8.

Bug: T368838
Change-Id: Ie8b38fc4f1ae416a950b448ef40d5d6902c140b5

setup.py

@@ -64,7 +64,6 @@
         'flake8-print>=5.0.0',
         'flake8-quotes>=3.3.2',
         'flake8-raise',
-        'flake8-string-format; python_version < "3.14"',  # T368838
         'flake8-tuple>=0.4.1',
         'flake8-no-u-prefixed-strings>=0.2',
         'pep8-naming==0.13.3; python_version < "3.8"',

tox.ini

@@ -126,9 +126,6 @@ deps =
 # H404: docstring multiline start
 # H405: docstring summary line
 # H903: Use only UNIX style newlines, not Windows style
-# P101: format string does contain unindexed parameters
-# P102: docstring does contain unindexed parameters
-# P103: other string does contain unindexed parameters
 # R100: raise in except handler without from
 # W503: line break before binary operator; against current PEP 8 recommendation
 
@@ -140,7 +137,7 @@ deps =
 # DARXXX: Darglint docstring issues to be solved
 # DAR000: T368849
 
-ignore = B007,D105,D211,D401,D413,D412,DAR000,DAR003,DAR101,DAR102,DAR201,DAR202,DAR301,DAR401,DAR402,DAR501,H101,H231,H232,H233,H234,H235,H236,H237,H238,H301,H306,H404,H405,H903,P101,P102,P103,P205,R100,W503
+ignore = B007,D105,D211,D401,D413,D412,DAR000,DAR003,DAR101,DAR102,DAR201,DAR202,DAR301,DAR401,DAR402,DAR501,H101,H231,H232,H233,H234,H235,H236,H237,H238,H301,H306,H404,H405,H903,R100,W503
 enable-extensions = H203,H204,H205,N818
 
 count = True