Bug 1340741. Nix the unused ::-moz-buttonlabel anonymous box. r=manishearth

MozReview-Commit-ID: IzXG8cCJoX0

--HG--
extra : rebase_source : 4728723b29698fee5cdfaff41033ab3e430a86ee

layout/style/nsCSSAnonBoxList.h

@@ -39,7 +39,6 @@ CSS_ANON_BOX(verticalFramesetBorder, ":-moz-vframeset-border")
 CSS_ANON_BOX(mozLineFrame, ":-moz-line-frame")
 
 CSS_ANON_BOX(buttonContent, ":-moz-button-content")
-CSS_ANON_BOX(mozButtonLabel, ":-moz-buttonlabel")
 CSS_ANON_BOX(cellContent, ":-moz-cell-content")
 CSS_ANON_BOX(dropDownList, ":-moz-dropdown-list")
 CSS_ANON_BOX(fieldsetContent, ":-moz-fieldset-content")