Bug 576496: Platform documentation shows outdated screenshots

Delete more screenshots when you don't add much value.

Change-Id: Ic4c1181e5aee05d64a1d78f1728bd698a4dbf37e
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.common/+/187393
Tested-by: Matthias Becker <ma.becker@sap.com>
Reviewed-by: Matthias Becker <ma.becker@sap.com>