remove icon element as unused (merge from trunk, https://trac.osgeo.org/grass/changeset/62180)

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@62528 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/manage/element_list

@@ -23,7 +23,6 @@ dig:oldvect:old vector:old (GRASS 5.0) vector map(s)
   dig_misc:misc
   reg:point registration
 dig_ascii:asciivect:asciivector:ASCII vector map(s)
-icons:icon:icon:paint icon file(s)
 paint/labels:labels:label:paint label file(s)
 site_lists:sites:site list:site list file(s)
 windows:region:region definition:region definition(s)