Remove excessive word counts

[AndrewKvalheim]

Checklist

• I have read the Contribution & Best practices Guide.
• My branch is up-to-date with the upstream master branch.
• The tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works (if appropriate).
• I have added necessary documentation (if appropriate).

Short description of what this resolves

Typing in the proposal’s abstract field gradually causes the browser to slow down and eventually become unresponsive. This is caused by duplicate event listeners being registered during every count, increasing the number of counts that take place every time the user types.

Changes proposed in this pull request

• OSEM already handles setup of the event listener, so use Countable#once instead of Countable#live.
• The input event is widely supported now, so remove the redundant alternatives.