multimedia/gstreamer1-editing-services: drop unused dependency after e3b732b4791c

Dependency gst-validate-1.0 found: NO found 1.16.3 but need: '>= 1.20.0'
Did not find CMake 'cmake'
Found CMake: NO
Run-time dependency gst-validate-1.0 found: NO (tried pkgconfig and cmake)
Looking for a fallback subproject for the dependency gst-validate-1.0
Neither a subproject directory nor a gst-devtools.wrap file was found.

PR: 270361
Reported by: antoine (via exp-run)