- This reverts commit 61dffa45.
- The assumption (from the reverted commit) that:
    Adding pymodule_PYTHON and pybin_scripts as prerequisites of 'all' rule should
    achieve the same thing as adding them to BUILT_SOURCES, but without deletion
  is incorrect: at least 'check' and 'install' also trigger BUILT_SOURCES, so anyone
  running just 'make install' (without running 'make' i.e. 'make all' first) would
  not build any of the Python scripts.