adwaita-icon-theme: do not delete symbolic svg but pack them in ${PN}-symbolic

adwaita-icon-theme: do not delete symbolic svg but pack them in ${PN}-symbolic

This fixes:
* gtk-icon-browser: for symbolic view almost all icons were missing
* xfce's thunar: 'home' and 'up' icons were missing. Had a long discussion with
  XFCE-people [1] and asked here [2].

How could I overlook the most obvious...

[1] https://bugzilla.xfce.org/show_bug.cgi?id=14443
[2] http://lists.openembedded.org/pipermail/openembedded-core/2018-November/275815.html

Signed-off-by: Andreas Müller <schnitzeltony@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>