Remove GNU make-ish.

Makefile

@@ -3,11 +3,7 @@ PYFLAKES = pyflakes
 PEP8 = pep8
 SETUP = $(PYTHON) setup.py
 PYDOCTOR ?= pydoctor
-ifeq ($(shell $(PYTHON) -c "import sys; print(sys.version_info >= (2, 7))"),True)
 TESTRUNNER ?= unittest
-else
-TESTRUNNER ?= unittest2.__main__
-endif
 RUNTEST = PYTHONHASHSEED=random PYTHONPATH=.:$(PYTHONPATH) $(PYTHON) -m $(TESTRUNNER)
 
 DESTDIR=/