Remove packageNameToUnqualComponentName

```
-- | Converts a package name to an unqualified component name
--
-- Useful in legacy situations where a package name may refer to an internal
-- component, if one is defined with that name.
--
-- @since 2.0.0.2
packageNameToUnqualComponentName :: PackageName -> UnqualComponentName
```

Yet, These "legacy" situations are not legacy. We can `build-depends` on the internal library. However now dependency contains `Set LibraryName`, and we should use that. I.e. the parser could/should already elaborate `build-depends` or `build-tool-depends`.

cc @fgaz @ezyang

Search the repository for packageNameToUnqualComponentName and inspect the parser handling of build-depends and build-tool-depends, including the Set LibraryName dependency data. The work is complete when the obsolete function and its uses are removed and dependency handling uses the existing library-name information.

Written by the indexing model from the issue text.