Disambiguate string-literals

GHC fails type-inference with `OverloadedStrings` + `Data.Foldable.elem`
otherwise.
Revert "Followup changes to addition of -fwarn-context-quantification"

This reverts commit 4023817d7c0e46db012ba2eea28022626841ca9b temporarily
as the respective feature hasn't landed in GHC HEAD yet, but this commit
blocks later commits from being referenced in GHC HEAD.