Don't call PythonInterp.cmake in KF5I18NMacros.
Summary:
Due to CMake caching the variables, anything depending on ki18n would be
unable to call find_package(PythonInterp) with a specific version.
Instead we just hardcode the python executable path.
Test Plan:
- Downloaded, installed a tarball with translations.
- The python2 backend in cantor doesn't claim python 2.7 was found if it's not true.
Subscribers: Build System, Frameworks
Tags: Frameworks, Build System
Differential Revision: https://phabricator.kde.org/D11176