Remove obsolete oceanic city gfx tags from city styles in ruledit to make it compile again

Patch by Emmet Hikory <persia>
Reported by Emmet Hikory <persia>

See bug #21886

git-svn-id: svn://svn.gna.org/svn/freeciv/trunk@24748 a0f10bec-cc02-0410-94fc-a9cfff90b4cd