Remove outdated Firefox workaround from reindeer in Tabsheet.

Author: Ansku

themes/src/main/themes/VAADIN/themes/reindeer/tabsheet/tabsheet-normal-style.scss

@@ -55,13 +55,6 @@
 	font-size: 14px;
 	font-weight: normal;
 }
-.v-ff & .#{$primaryStyleName}-caption-close{
-	margin-top: -17px;
-}
-
-.v-ff & .#{$primaryStyleName}-caption-close:only-child {
-    margin-top: -1px;
-}
 
 
 .#{$primaryStyleName}-caption-close:hover {