glade3: disable help, fails to build

* fixes:
| http://www.oasis-open.org/docbook/xml/4.1.2/ent/iso-grk1.ent:1: validity error : All markup of the conditional section is not in the same entity
| HTTP/1.1 200 OK
|    ^
| http://www.oasis-open.org/docbook/xml/4.1.2/ent/iso-grk1.ent:1

: parser error : Content error in the external subset
| HTTP/1.1 200 OK
|       ^
| unable to parse sl/glade3.xml
| make[2]: *** [glade3-sl.omf] Error 1
| make[2]: *** Waiting for unfinished jobs....
| make[2]: Leaving directory `/OE/jansa-test/shr-core/tmp-eglibc/work/armv5te-oe-linux-gnueabi/glade3/3.8.2-r0/glade3-3.8.2/help'

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>