* Migrate the patches for `doctest`, `free`, `persistent`, and `yesod-core`
  to the latest versions on Hackage.
* Remove the patches for `Cabal`, `bytes`, `cabal-doctest`, `ghc-paths`,
  `hsc2hs`, `polyparse`, `singleton-nats`, `tar`, `yaml`, and `zlib`, as
  more recent versions of these packages (that support GHC 8.8 and HEAD)
  are now available on Hackage.

I opted not to remove the `th-desugar-1.9`/`singletons-2.5.1` patches for
now, even though they are not the latest Hackage releases, since upgrading
them can be a nontrivial process (similar to the `primitive-0.6`/`-0.7`
situation).