Some cleanup to recent type computable inlining changes (#3169)
Some cleanup to recent type computable inlining changes (#3169)

PR #3165 added an assert that the stype was a view, but exempted
mutations from that check. Exempting mutations is spurious and
unnecessary (though it seemed necessary at one point during
development).
edgedb/edgedb,edgedb/edgedb,edgedb/edgedb