Remove pytest-pycodestyle dependency.

The pytest-pycodestyle package is now a Python 3.6+ dependency, so it will
fail on 3.5. But even so, we don't need it, as flake8 (already ran as part
of pre-commit) already runs codestyle.

Author: Flameeyes

.travis.yml

@@ -17,4 +17,4 @@ install:
   - pip install .[dev]
 
 script:
-  - py.test -vvv --pycodestyle --cov=pcapng --cov-report=term-missing tests
+  - py.test -vvv --cov=pcapng --cov-report=term-missing tests

setup.cfg

@@ -31,7 +31,6 @@ dev =
     pre-commit
     pytest>=5.4
     pytest-cov
-    pytest-pycodestyle
     setuptools_scm[toml]
     sphinx
     sphinx-rtd-theme