Bug 1891458 - Remove missing_header patch r=media-playback-reviewers,padenot

The missing_header patch has been uplifted and merged in the upstream
[1], so there is no need to patch it locally.

[1] https://chromium-review.googlesource.com/c/webm/libvpx/+/5425372

Differential Revision: https://phabricator.services.mozilla.com/D207805

media/libvpx/missing_header.patch

@@ -1,12 +0,0 @@
-Add missing header for EBUSY
-
---- a/vpx_util/vpx_pthread.h
-+++ b/vpx_util/vpx_pthread.h
-@@ -26,6 +26,7 @@ extern "C" {
- #define NOMINMAX
- #undef WIN32_LEAN_AND_MEAN
- #define WIN32_LEAN_AND_MEAN
-+#include <errno.h>    // NOLINT
- #include <process.h>  // NOLINT
- #include <stddef.h>   // NOLINT
- #include <windows.h>  // NOLINT

media/libvpx/moz.yaml

@@ -56,7 +56,6 @@ vendoring:
     - arm_cpu_runtime_detection_code_on_openbsd.patch
     - input_frame_validation.patch
     - input_frame_validation_vp9.patch
-    - missing_header.patch
 
   update-actions:
     - action: move-file