Revert "gstlal_inspiral_compute_dtdphideff_cov_matrix: fix import. dont push before coffee"

This supersedes MR !64 (closed) and reverts previous pushes to master that had unintended consequences. This does run end to end and produces sensible dtdphi files as far as I can tell. While the previous fix made dtdphi files, they did not contain correct data.