python: Use relative URLs for pyln-{client,proto,testing}

This allows to not have to worry about the source of the installation,
and we always use our in-tree version. It also means we pull in the
requirements.txt files through the setup.py and don't need to
replicate them.

requirements.txt

@@ -4,36 +4,11 @@ https://github.com/ElementsProject/libwally-core/releases/download/release_0.8.0
 https://github.com/ElementsProject/libwally-core/releases/download/release_0.8.0/wallycore-0.8.0-cp37-cp37m-macosx_10_14_x86_64.whl; sys_platform == 'darwin' and python_version == '3.7'
 mrkd ~= 0.1.6
 Mako ~= 1.1.3
+flake8 ~= 3.7.8
 
-# Dependencies from pyln-client
-Sphinx ~= 3.4.0
-flake8==3.7.8
-recommonmark>=0.7.*
-sphinx-rtd-theme==0.4.2
-sphinxcontrib-websupport==1.1.0
-tqdm==4.32.2
-
-# Dependencies from pyln-testing
-Flask==1.1.*
-cheroot==8.5.*
-ephemeral-port-reserve==1.1.1
-filelock==3.0.*
-flaky ~= 3.7.0
-psutil==5.7.*
-psycopg2-binary==2.8.*
-pytest-rerunfailures==9.1.1
-pytest-timeout ~= 1.4.2
-pytest-xdist ~= 2.2.0
-pytest==6.1.*
-python-bitcoinlib==0.11.*
-
-# Dependencies from pyln-proto
-base58 ~= 2.0.1
-bitstring ~= 3.1.6
-coincurve ~= 13.0.0
-cryptography ~= 3.2
-mypy ~= 0.790
-pysocks ~= 1.7.1
+./contrib/pyln-client
+./contrib/pyln-proto
+./contrib/pyln-testing
 
 # Dependencies from pyln-spec
 # None