Remove unused `extract_source()` method
Remove unused `extract_source()` method

It looks like it was dropped long time ago.
kivy/python-for-android,rnixx/python-for-android,germn/python-for-android,ibobalo/python-for-android,germn/python-for-android,kronenpj/python-for-android,PKRoma/python-for-android,ibobalo/python-for-android,kronenpj/python-for-android,kronenpj/python-for-android,ibobalo/python-for-android,kivy/python-for-android,ibobalo/python-for-android,kivy/python-for-android,ibobalo/python-for-android,rnixx/python-for-android,rnixx/python-for-android,rnixx/python-for-android,wexi/python-for-android,wexi/python-for-android,kivy/python-for-android,wexi/python-for-android,germn/python-for-android,rnixx/python-for-android,kronenpj/python-for-android,wexi/python-for-android,kivy/python-for-android,germn/python-for-android,kronenpj/python-for-android,ibobalo/python-for-android,rnixx/python-for-android,PKRoma/python-for-android,wexi/python-for-android,PKRoma/python-for-android,PKRoma/python-for-android,germn/python-for-android,PKRoma/python-for-android,germn/python-for-android,wexi/python-for-android