Revert UMD (#13772 & friends) for now, due to #13812.

Will hopefully revert this reversion and land a fully-working version of UMD in v3.3.0.

Revert "some changes from #13801 - add strict mode back and =="
This reverts commit 2b302f69eea416bc85e7827b7d7a74d49f879662.

Revert "Fix regression of #10038 introduced by #13772"
This reverts commit e9d6756a1ac76a9db31a41e8e03f663bedc41b70.

Revert "MD/CommonJS/Globals #12909"
This reverts commit 1c6fa9010daf0d0c21de9e20fe6ac4dba1788d90.

Revert "address #13811"
This reverts commit f347d7d955bbb17234b8e12c68efae7d516ce62c.

Conflicts:
    js/carousel.js
    js/collapse.js
    js/dropdown.js
    js/modal.js
    js/tab.js
    js/tooltip.js
Merge pull request #13904 from twbs/revert-umd

Revert UMD for now, due to #13812.