Avoid `type_sum()` reexport

[krlmlr]

Users should import it from pillar (or tibble if absolutely necessary), or better implement vec_ptype_abbr() .

dplyr also reexports many more functions that are now deprecated.

This is a breaking change.

[hadley]

See discussion in #6281

[DavisVaughan]

To summarize, in https://github.com/tidyverse/dplyr/pull/6284 I removed the tbl_sum() re-export, but type_sum() is imported into many other packages through dplyr and will be hard to remove https://github.com/tidyverse/dplyr/pull/6281#issuecomment-1137739984

[krlmlr]

Yeah, let's keep the reexport. I wish there was a way to simplify this. We could notify maintainers now, and plan for a breaking patch release (1.1.1 or 1.1.2) in a month or so from now, with just that change. But that seems so much work for so limited gain. I gave up on similar issues for pillar/tibble.