Install linters exclusively via pip

[emersonknapp]

Fixes #109

In preparation for moving over to a pure-python package, this PR removes all rosdep dependency requirements.

• Explicitly require the same set of linters and pytest runners specified in the ROS2 source installation guide https://index.ros.org/doc/ros2/Installation/Eloquent/Linux-Development-Setup/
• Add coveragerc to omit eggs, because locally the automatic coverage run (via pytest-cov) was taking a long time specifically looking at that directory that is now automatically created (.gitignore does not affect this)
• Remove all package dependencies from package.xml

Signed-off-by: Emerson Knapp emerson.b.knapp@gmail.com

[emersonknapp]

There is an issue with the CI environment and the URL-based setuptools requirements - I am working on it and you can hold off reviewing until the checks are passing

[codecov[bot]]

Codecov Report

Merging #117 into master will decrease coverage by 1.65%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #117      +/-   ##
==========================================
- Coverage   87.36%   85.71%   -1.66%     
==========================================
  Files           6        9       +3     
  Lines         372      392      +20     
  Branches        0       23      +23     
==========================================
+ Hits          325      336      +11     
  Misses         47       47              
- Partials        0        9       +9

Flag	Coverage Δ
#unittests	85.71% <ø> (-1.66%)	:arrow_down:

Impacted Files	Coverage Δ
test/test_colcon_mixins.py	88.23% <0%> (-5.89%)	:arrow_down:
cross_compile/sysroot_compiler.py	77.09% <0%> (-3.92%)	:arrow_down:
cross_compile/ros2_cross_compile.py	66.66% <0%> (-2.57%)	:arrow_down:
test/test_flake8.py	100% <0%> (ø)
test/test_copyright.py	100% <0%> (ø)
test/test_pep257.py	100% <0%> (ø)

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[emersonknapp]

Closing in favor of a more comprehensive switch to a non-ros package - which has a much simpler solution for this detail of it