Use ReadTheDocs install.path

.readthedocs.yml

@@ -8,3 +8,4 @@ python:
   version: 3.7  # Keep in sync with .travis.yml
   install:
     - requirements: docs/requirements.txt
+    - path: .

docs/requirements.txt

@@ -2,18 +2,3 @@ Sphinx>=2.1
 sphinx-hoverxref
 sphinx-notfound-page
 sphinx_rtd_theme
-
-# Required for ReadTheDocs
-# Keep in sync with setup.py
-Twisted>=17.9.0
-cryptography>=2.0
-cssselect>=0.9.1
-lxml>=3.5.0
-parsel>=1.5.0
-PyDispatcher>=2.0.5
-pyOpenSSL>=16.2.0
-queuelib>=1.4.2
-service_identity>=16.0.0
-w3lib>=1.17.0
-zope.interface>=4.1.3
-protego>=0.1.15

setup.py

@@ -62,7 +62,6 @@ setup(
         'Topic :: Software Development :: Libraries :: Python Modules',
     ],
     python_requires='>=3.5',
-    # Keep in sync with docs/requirements.txt
     install_requires=[
         'Twisted>=17.9.0',
         'cryptography>=2.0',