* gnu/packages/lxde.scm (lxpanel)[source]: Use mirror URI.
[configure-flags]: Add --enable-gtk3.
[phases]{wrap}: Use search-input-file and this-package-input.
[inputs]: Use new style inputs. Replace gtk+-2 with gtk+. Remove
libindicator comment; it seems to expect an old incompatible version.
Sort in lexical order. Add bash-minimal.
[native-inputs]: Use new style inputs. Sort in lexical order.
[propagated-inputs]: Likewise.