This patch removes infrastructure and ui for DebuggingHelpers
and specifically qmldumptool.

The qmldumptool was the last relevant DebuggingHelper and is only required
for Qt < 4.8.

Change-Id: I3767be0858e5eba16a33a3ab8436e95fc06a9e99
Reviewed-by: hjk <hjk@theqtcompany.com>