Make InstalledUnitId be ONLY a FastString.
It turns out that we don't really need to be able to extract a ComponentId from UnitId, except in one case. So compress UnitId into a single FastString. The one case where we do need the ComponentId is when we are compiling an instantiated version of a package; we need the ComponentId to look up the indefinite version of this package from the database. So now we just pass it in as an argument -this-component-id. Also: ghc-pkg now no longer will unregister a package if you register one with the same package name, if the instantiations don't match. Cabal submodule update which tracks the same data type change. Signed-off-by: Edward Z. Yang <email@example.com>