Remove markdownlint

Author: adamtheturtle

CONTRIBUTING.md

@@ -12,12 +12,6 @@ Install Python dependencies in a virtual environment.
 pip install --editable .[dev]
 ```
 
-Insall `npm` dependencies for linting Markdown files:
-
-```sh
-npm install -g markdownlint-cli
-```
-
 Spell checking requires `enchant`.
 This can be installed on macOS, for example, with [Homebrew](http://brew.sh):
 
@@ -31,8 +25,6 @@ and on Ubuntu with `apt`:
 apt-get install -y enchant
 ```
 
-and to lint
-
 ## Linting
 
 Run lint tools:

Makefile

@@ -12,7 +12,6 @@ lint:
 	pyroma .
 	vulture . --min-confidence 100
 	yapf --diff --recursive src/ tests/ ci/
-	markdownlint --config .markdownlint.json README.md CONTRIBUTING.md
 
 .PHONY: fix-lint
 fix-lint: