qtwebkit: remove examples packages

* fixes:
  NOTE: multiple providers are available for runtime qtwebkit-examples (qtwebkit-examples, qtwebkit)
  NOTE: consider defining a PREFERRED_PROVIDER entry to match qtwebkit-examples
  NOTE: multiple providers are available for runtime qtwebkit-examples-dev (qtwebkit, qtwebkit-examples)
  NOTE: consider defining a PREFERRED_PROVIDER entry to match qtwebkit-examples-dev

Backported from meta-qt5 rev. 284020d9344b6fbd88d9c6d5ff6fbaef430a775b
Author: Martin Jansa <Martin.Jansa@gmail.com>

JIRA: MEIP-356

Signed-off-by: Mikhail Durnev <Mikhail_Durnev@mentor.com>