refactor(deps): remove requirements.txt

install_requires from setup.cfg counts as the dependencies end users
install anyway, so we don't want to pin the runtime dependencies that
tightly in tests. Better let them fail in tests if they fail for a
reason for some dep version.

Refs https://packaging.python.org/discussions/install-requires-vs-requirements/

Author: scop

requirements.txt

@@ -9,14 +9,12 @@ skip_missing_interpreters = True
 
 [testenv]
 commands = py.test test/
-deps = -rrequirements.txt
-       -rrequirements-dev.txt
+deps = -rrequirements-dev.txt
 
 [testenv:integration]
 passenv = *
 commands = py.test test/ {posargs: -x}
-deps = -rrequirements.txt
-       -rrequirements-dev.txt
+deps = -rrequirements-dev.txt
 
 [flake8]
 ignore = D100,  # missing docstring in public module