chore: remove upstreamed ffmpeg patch (#18524)

patches/common/config.json

@@ -3,7 +3,5 @@
 
   "src/electron/patches/common/boringssl": "src/third_party/boringssl/src",
 
-  "src/electron/patches/common/ffmpeg": "src/third_party/ffmpeg",
-
   "src/electron/patches/common/v8":  "src/v8"
 }

patches/common/ffmpeg/.patches

@@ -1 +0,0 @@
-build_gn.patch

patches/common/ffmpeg/build_gn.patch

@@ -1,24 +0,0 @@
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Ales Pergl <alpergl@microsoft.com>
-Date: Mon, 22 Oct 2018 10:45:25 -0700
-Subject: build_gn.patch
-
-Chromium's Mac toolchain sets the "install_name" linker parameter only
-when "is_component_build" is true, but we want to set even if it's false,
-because we are making a dylib which will be distributed inside a bundle.
-
-diff --git a/BUILD.gn b/BUILD.gn
-index fd79bc4eaba90ab5e8c6df9942dbfaeeebabbc73..1e1859d5aa1567da8a768c870d8a477b052f50ec 100755
---- a/BUILD.gn
-+++ b/BUILD.gn
-@@ -397,6 +397,10 @@ if (is_component_ffmpeg) {
-     # So we can append below and assume they're defined.
-     ldflags = []
- 
-+    if (!is_component_build && is_mac) {
-+      ldflags += [ "-Wl,-install_name,@rpath/libffmpeg.dylib" ]
-+    }
-+
-     if (is_fuchsia || (is_posix && !is_mac)) {
-       # Fixes warnings PIC relocation when building as component.
-       ldflags += [