[BUGFIX] EM: avoid cropping action columns

In some browsers the action icons of the new EM disappear, to be
replaced by an ellipsis (...). This is due to ExtJS using
"text-overflow: ellipsis" and some browsers miscalculating the
width of the column. This text-overflow directive is not necessary
as the icons fit nicely anyway.

Change-Id: I35aa04191f1f315e1e3ac7c22057d205bb0393b2
Fixes: #30900
Releases: 6.0, 4.7, 4.6, 4.5
Reviewed-on: http://review.typo3.org/10809
Reviewed-by: Francois Suter
Tested-by: Francois Suter