Remove legacy resolver

Makefile

@@ -7,7 +7,8 @@ all: test
 install:
 	@$(call doc,$@:)
 	@pip install --upgrade pip setuptools
-	@pip install --editable .[dev] --upgrade --use-deprecated=legacy-resolver
+	@pip install --requirement requirements/dev --upgrade
+	@pip install --editable . --upgrade --no-dependencies
 
 ## Install openfisca-core for deployment and publishing.
 build: setup.py

requirements/dev

@@ -1,7 +1,16 @@
 # Please make sure to pin all dependency versions, in order to avoid unwanted
 # functional and integration breaks caused by external code updates.
 #
-# These are dev dependencies, so pin them.
+# General Rule
+# ============
+#
+# * Pin them.
+#
+# Exceptions
+# ==========
+#
+# * openfisca-country-template should not be constrained (circular dep).
+# * openfisca-extension-template should not be constrained (circular dep).
 
 # For automatic style formatting.
 autopep8 == 1.5.7
@@ -18,8 +27,8 @@ pytest-cov == 2.11.1
 mypy == 0.812
 
 # For testing: parameters, variables, etc.
-openfisca-country-template == 3.12.5
-openfisca-extension-template == 1.3.6
+openfisca-country-template
+openfisca-extension-template
 
 # Include Web API dependencies for development
 -r web-api

requirements/tracker

@@ -2,4 +2,4 @@
 # versions.
 
 # For sending usage statistics to the Matomo third-party service.
-openfisca-tracker <= 0.4.0
+openfisca-tracker