[GTK] Remove unused GSettings stuff

[GTK] Remove unused GSettings stuff
https://bugs.webkit.org/show_bug.cgi?id=78995

Reviewed by Martin Robinson.

.:

* configure.ac: remove gsettings schema file creation.

Source/WebKit/gtk:

* GNUmakefile.am: remove GSettings-related stuff.
* WebCoreSupport/InspectorClientGtk.cpp:
(WebKit): Remove unused code.
* org.webkitgtk.gschema.xml.in: Removed.
* webkit/webkitwebinspector.cpp:
(webkit_web_inspector_execute_script): remove gsettings-related helper.
* webkit/webkitwebinspectorprivate.h: Ditto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108190 268f45cc-cd09-0410-ab3c-d52691b4dbfc