Fix 6 Flake8 issues (#6541)

* F541

* F821

* F841

* E741

* E302

* E722

* Apply suggestions from code review

* Update general.py

* Update datasets.py

* Update export.py

* Update plots.py

* Update plots.py

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

setup.cfg

@@ -30,10 +30,6 @@ ignore =
     E731  # Do not assign a lambda expression, use a def
     F405  # name may be undefined, or defined from star imports: module
     E402  # module level import not at top of file
-    F841  # local variable name is assigned to but never used
-    E741  # do not use variables named ‘l’, ‘O’, or ‘I’
-    F821  # undefined name name
-    E722  # do not use bare except, specify exception instead
     F401  # module imported but unused
     W504  # line break after binary operator
     E127  # continuation line over-indented for visual indent
@@ -41,8 +37,6 @@ ignore =
     E231  # missing whitespace after ‘,’, ‘;’, or ‘:’
     E501  # line too long
     F403  # ‘from module import *’ used; unable to detect undefined names
-    E302  # expected 2 blank lines, found 0
-    F541  # f-string without any placeholders
 
 
 [isort]