Unbreak USES=gecko:seamonkey as www/seamonkey is still at 2.32.x

Leaving www/linux-seamonkey at 2.33b1 for now. VuXML still marks it as
vulnerable, so updating is discouraged but should be harmless unless
seamonkey-i18n is also used. 2.33 release should happen in a few
days (2015-03-02 per bug 1137028).

MFH: 2015Q1
X-MFH-With: r380090