Revert "Merge branch 'symengine' into 'master'"

This reverts merge request !26 (merged)

enabled an automatic merge when the pipeline for 195e15c0 succeeds

cc @mattwala

Reverting because of these failures: pytential!12 (builds)

merged

mentioned in commit 41712001

mentioned in commit 4e9d1eb1

mentioned in merge request !32 (merged)