Drop after multimedia/gstreamer1-plugins is updated to 1.18 or later

Package dependency requirement 'gstreamer-1.0 >= 1.18' could not be satisfied.
Package 'gstreamer-1.0' has version '1.16.2', required version is '>= 1.18'

error[E0599]: no method named `pull_until_eos` found for struct `Harness` in the current scope
   --> audio/audiofx/tests/ebur128level.rs:113:33
    |
113 |     while let Some(_buffer) = h.pull_until_eos().unwrap() {
    |                                 ^^^^^^^^^^^^^^ method not found in `Harness`

--- audio/audiofx/Cargo.toml
+++ audio/audiofx/Cargo.toml	2021-08-15 06:32:37.895468529 +0000
@@ -25,7 +25,7 @@ crate-type = ["cdylib", "rlib"]
 path = "src/lib.rs"
 
 [dev-dependencies]
-gst-check = { package = "gstreamer-check", version = "0.17", features = ["v1_18"] }
+gst-check = { package = "gstreamer-check", version = "0.17", features = ["v1_16"] }
 gst-app = { package = "gstreamer-app", version = "0.17" }
 
 [build-dependencies]
--- audio/audiofx/tests/ebur128level.rs.orig	2021-08-05 15:13:43 UTC
+++ audio/audiofx/tests/ebur128level.rs
@@ -110,7 +110,13 @@ fn run_test(layout: gst_audio::AudioLayout, format: gs
 
     // Pull all buffers until EOS
     let mut num_buffers = 0;
+    #[cfg(feature = "v1_18")]
     while let Some(_buffer) = h.pull_until_eos().unwrap() {
+        num_buffers += 1;
+    }
+    #[cfg(not(feature = "v1_18"))]
+    for _ in 0..5 {
+        h.pull().unwrap();
         num_buffers += 1;
     }
     assert_eq!(num_buffers, 5);