[BUGFIX] Commit parameter which is no longer available since Solr4 removed

The waitFlush parameter has been removed in Solr 4 and therefore the commit
function didn’t work and the Solr server throws an exception.
This parameter has been deactivated.

Resolves: #54249
Releases: 3.0
Change-Id: I373314f6564e72cc6b4b1b1849cebfdf40031b49
Reviewed-on: https://review.typo3.org/25984
Reviewed-by: Ingo Renner
Tested-by: Ingo Renner