Revert "Allow multiple delegated tooltip selectors on a node"

This reverts commit 1b3237629a316af41945e20837cf3a332798b264.
This reverts PR #14189 because it caused major regressions.

Fixes #15168.

We'll try to revisit #14167's feature request in Bootstrap v4.

[skip validator]
Merge pull request #15466 from twbs/revert-14189

Revert #14189 to fix #15168