chore(lib): remove customPropTypes.as

[layershifter]

We don't need anymore customPropTypes.as because it exists in prop-types as PropTypes.elementType 🎉

[codecov-io]

Codecov Report

Merging #3751 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3751   +/-   ##
=======================================
  Coverage   99.84%   99.84%           
=======================================
  Files         175      175           
  Lines        3125     3125           
=======================================
  Hits         3120     3120           
  Misses          5        5

Impacted Files	Coverage Δ
src/elements/List/List.js	100% <ø> (ø)	⬆️
src/elements/Button/ButtonGroup.js	100% <ø> (ø)	⬆️
src/modules/Sticky/Sticky.js	99.09% <ø> (ø)	⬆️
src/elements/List/ListList.js	100% <ø> (ø)	⬆️
src/modules/Search/SearchCategory.js	100% <ø> (ø)	⬆️
src/views/Card/Card.js	100% <ø> (ø)	⬆️
src/views/Item/ItemHeader.js	100% <ø> (ø)	⬆️
src/modules/Sidebar/SidebarPushable.js	100% <ø> (ø)	⬆️
src/views/Comment/Comment.js	100% <ø> (ø)	⬆️
src/views/Feed/FeedContent.js	100% <ø> (ø)	⬆️
... and 138 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9d428b0...8523362. Read the comment docs.