Remove some expected failures

We can remove several packages from the expected failures list due to recent developments:

• We can remove hashtables, http2, statistics, and unicode-transforms from the expected failures for 8.8 now that the fix for ghc#16288 (closed) has been backported to the ghc-8.8 branch.
• We can remove singletons and vinyl from the expected failures for master now that ghc!2102 (closed) has landed. The vinyl-0.12.0 patch needs to be updated since it uses TypeFamilyDependencies in such a way that requires UndecidableInstances. (Note that singletons already enabled UndecidableInstances in all the right places, so no further action is required for that library.)