build: Don't have both a pip and pip-tools requirements file.

pip-tools.txt pins pip and pip-tools to co-compatible versions. We don't
need a separate file to track and upgrade pip independently of
pip-tools.

Author: feanil

Makefile

@@ -66,7 +66,6 @@ detect_changed_source_translations: ## check if translation files are up-to-date
 	i18n_tool changed
 
 pre-requirements: ## install Python requirements for running pip-tools
-	pip install -r requirements/pip.txt
 	pip install -r requirements/pip-tools.txt
 
 local-requirements:
@@ -128,9 +127,6 @@ compile-requirements: pre-requirements $(COMMON_CONSTRAINTS_TXT) ## Re-compile *
 	pip-compile -v ${COMPILE_OPTS} -o requirements/pip-tools.txt requirements/pip-tools.in
 	pip install -r requirements/pip-tools.txt
 
-	pip-compile -v --allow-unsafe ${COMPILE_OPTS} -o requirements/pip.txt requirements/pip.in
-	pip install -r requirements/pip.txt
-
 	@ export REBUILD='--rebuild'; \
 	for f in $(REQ_FILES); do \
 		echo ; \