kernel-shark: Add destructor for KsGLWidget

Not sure how I missed to define this destructor before. The good
thing is that the GUI has only one GL widget, and this widget stays
alive for the whole duration of the program.

Link: http://lore.kernel.org/linux-trace-devel/20190314151012.905-8-ykaradzhov@vmware.com

Signed-off-by: Yordan Karadzhov <ykaradzhov@vmware.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
2 files changed