Revert "Better reverse mode propagation through implicit function (not ready), #823"

This reverts commit b2df813970ae02cf56acbda147064662b54cd582.
Revert "Better forward mode propagation through implicit function, #823"

This reverts commit 7a64425d45a91ea3c45227b514b3a4460c5cb683.
Revert "Added dummy ImplicitFunctionInternal::spEvaluate, #823"

This reverts commit 816f5ecbcf1da9a139e33795bfb7f561a7bab7af.
Revert "Test for #823"

This reverts commit 29dbf3c643cfff520950e7e72dd0ef43ef653193.
Revert "Better reverse mode propagation through linear solver, #889"

This reverts commit 9db0d310b50bf6f368d999eb49e580ca29d9599d.
Revert "Code readability, #889"

This reverts commit 05043925254cb65f01cfd133ba8f20bdf257ce95.
Revert "Better forward mode propagation through linear solver, #889"

This reverts commit a15a61184e47af1252663e65bd439947498f377f.