🔥 Remove unused Makefile variables (kivy#2985)

Author: AndreMiras

Makefile

@@ -3,14 +3,6 @@ PIP=$(VIRTUAL_ENV)/bin/pip
 TOX=`which tox`
 ACTIVATE=$(VIRTUAL_ENV)/bin/activate
 PYTHON=$(VIRTUAL_ENV)/bin/python
-FLAKE8=$(VIRTUAL_ENV)/bin/flake8
-PYTEST=$(VIRTUAL_ENV)/bin/pytest
-SOURCES=src/ tests/
-PYTHON_MAJOR_VERSION=3
-PYTHON_MINOR_VERSION=6
-PYTHON_VERSION=$(PYTHON_MAJOR_VERSION).$(PYTHON_MINOR_VERSION)
-PYTHON_MAJOR_MINOR=$(PYTHON_MAJOR_VERSION)$(PYTHON_MINOR_VERSION)
-PYTHON_WITH_VERSION=python$(PYTHON_VERSION)
 DOCKER_IMAGE=kivy/python-for-android
 ANDROID_SDK_HOME ?= $(HOME)/.android/android-sdk
 ANDROID_NDK_HOME ?= $(HOME)/.android/android-ndk