[BUGFIX] Fix update button in Extension Manager

The change If527b0e8fd77a059c8b25db16a926c5c80356331 introduced
a regression which broke the event listeners for the update buttons.
Change the JavaScript code to match the new markup.

Resolves: #65580
Releases: master
Change-Id: Ifbf857c88fad10f6e0411c48dadacf85bcfa425c
Reviewed-on: http://review.typo3.org/37612


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>