Remove the servo-gst-plugin (#30976)

The CI doesn't build this by default and it's currently unused. It is
one thing that's currently making it a bit trickier to allow for
non-mach builds of Servo.

Cargo.lock

@@ -2255,16 +2255,6 @@ dependencies = [
  "bitflags 2.4.1",
 ]
 
-[[package]]
-name = "gst-plugin-version-helper"
-version = "0.2.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "cc81ae3a09f23761eb3b122f50e5daedea4b44fdf8242ec133bc87aa8e24f9b8"
-dependencies = [
- "chrono",
- "toml",
-]
-
 [[package]]
 name = "gstreamer"
 version = "0.15.7"
@@ -5156,30 +5146,6 @@ dependencies = [
  "time-point",
 ]
 
-[[package]]
-name = "servo-gst-plugin"
-version = "0.0.1"
-dependencies = [
- "cfg-if 1.0.0",
- "crossbeam-channel",
- "euclid",
- "glib",
- "gst-plugin-version-helper",
- "gstreamer",
- "gstreamer-base",
- "gstreamer-gl",
- "gstreamer-gl-sys",
- "gstreamer-sys",
- "gstreamer-video",
- "lazy_static",
- "libservo",
- "log",
- "servo-media",
- "sparkle",
- "surfman",
- "webxr",
-]
-
 [[package]]
 name = "servo-media"
 version = "0.1.0"