Revert "Fix pkgconfig wraning about datadir"

This reverts commit b0dcf318701e517340aa7a491af8a8384df474a4.
Properly fix dataroot warning for pkg-config file.

All we needed to do was add @dataroot@ to caja-python.pc.in.

config.status: WARNING:  'caja-python.pc.in' seems to ignore the
--datarootdir setting