Revert "`exprOkForSpeculation` for Note [IO hack in the demand analyser]"
Revert "`exprOkForSpeculation` for Note [IO hack in the demand analyser]"

This reverts commit ce64b397777408731c6dd3f5c55ea8415f9f565b on the
grounds of the regression it would introduce in a couple of packages.

Fixes #17653.

Also undoes a slight metric increase in #13701 introduced by that commit
that we didn't see prior to !1983.

Metric Decrease:
    T13701

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc