evince: disable help build

* xsltproc does not work in oe-core correctly:
  | xsltproc -o evince-it.omf --stringparam db2omf.basename evince --stringparam db2omf.format 'docbook' --stringparam db2omf.dtd "-//OASIS//DTD DocBook XML V4.1.2//EN" --stringparam db2omf.lang it --stringparam db2omf.omf_dir "/usr/share/omf" --stringparam db2omf.help_dir "/usr/share/gnome/help" --stringparam db2omf.omf_in "/OE/jansa-test/shr-core/tmp-eglibc/work/armv5te-oe-linux-gnueabi/evince/2.32.0-r2/evince-2.32.0/help/evince.omf.in"  /OE/jansa-test/shr-core/tmp-eglibc/sysroots/qemuarm`/OE/jansa-test/shr-core/tmp-eglibc/sysroots/x86_64-linux/usr/bin/pkg-config --variable db2omf gnome-doc-utils` it/evince.xml || { rm -f "evince-it.omf"; exit 1; }
  | http://www.oasis-open.org/docbook/xml/4.1.2/dbhierx.mod:115: parser warning : PEReference: %list.class; not found
  |               %local.divcomponent.mix;">
  |                                        ^
  ...
* https://bugzilla.yoctoproject.org/show_bug.cgi?id=2416



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