Remove gulp-multi-process

This package has not been used since #8140. We now spawn separate
processes directly in our build script rather than using this gulp
plugin to do so.

package.json

@@ -245,7 +245,6 @@
     "gulp-debug": "^3.2.0",
     "gulp-imagemin": "^6.1.0",
     "gulp-livereload": "4.0.0",
-    "gulp-multi-process": "^1.3.1",
     "gulp-rename": "^2.0.0",
     "gulp-replace": "^1.0.0",
     "gulp-rtlcss": "^1.4.0",

yarn.lock

@@ -4518,55 +4518,6 @@ async-settle@^1.0.0:
   dependencies:
     async-done "^1.2.2"
 
-async.queue@^0.5.2:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/async.queue/-/async.queue-0.5.2.tgz#8d5d90812e1481066bc0904e8cc1712b17c3bd7c"
-  integrity sha1-jV2QgS4UgQZrwJBOjMFxKxfDvXw=
-  dependencies:
-    async.util.queue "0.5.2"
-
-[email protected]:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/async.util.arrayeach/-/async.util.arrayeach-0.5.2.tgz#58c4e98028d55d69bfb05aeb3af44e0a555a829c"
-  integrity sha1-WMTpgCjVXWm/sFrrOvROClVagpw=
-
-[email protected]:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/async.util.isarray/-/async.util.isarray-0.5.2.tgz#e62dac8f2636f65875dcf7521c2d24d0dfb2bbdf"
-  integrity sha1-5i2sjyY29lh13PdSHC0k0N+yu98=
-
-[email protected]:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/async.util.map/-/async.util.map-0.5.2.tgz#e588ef86e0b3ab5f027d97af4d6835d055ca69d6"
-  integrity sha1-5YjvhuCzq18CfZevTWg10FXKadY=
-
-[email protected]:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/async.util.noop/-/async.util.noop-0.5.2.tgz#bdd62b97cb0aa3f60b586ad148468698975e58b9"
-  integrity sha1-vdYrl8sKo/YLWGrRSEaGmJdeWLk=
-
-[email protected]:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/async.util.onlyonce/-/async.util.onlyonce-0.5.2.tgz#b8e6fc004adc923164d79e32f2813ee465c24ff2"
-  integrity sha1-uOb8AErckjFk154y8oE+5GXCT/I=
-
-[email protected]:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/async.util.queue/-/async.util.queue-0.5.2.tgz#57f65abe1a3cdf273d31abd28ab95425f8222ee5"
-  integrity sha1-V/Zavho83yc9MavSirlUJfgiLuU=
-  dependencies:
-    async.util.arrayeach "0.5.2"
-    async.util.isarray "0.5.2"
-    async.util.map "0.5.2"
-    async.util.noop "0.5.2"
-    async.util.onlyonce "0.5.2"
-    async.util.setimmediate "0.5.2"
-
-[email protected]:
-  version "0.5.2"
-  resolved "https://registry.yarnpkg.com/async.util.setimmediate/-/async.util.setimmediate-0.5.2.tgz#2812ebabf2a58027758d4bc7793d1ccfaf10255f"
-  integrity sha1-KBLrq/KlgCd1jUvHeT0cz68QJV8=
-
 [email protected]:
   version "0.9.2"
   resolved "https://registry.yarnpkg.com/async/-/async-0.9.2.tgz#aea74d5e61c1f899613bf64bda66d4c78f2fd17d"
@@ -12718,13 +12669,6 @@ [email protected]:
     tiny-lr "^1.1.1"
     vinyl "^2.2.0"
 
-gulp-multi-process@^1.3.1:
-  version "1.3.1"
-  resolved "https://registry.yarnpkg.com/gulp-multi-process/-/gulp-multi-process-1.3.1.tgz#e12aa818e4c234357ad99d5caff8df8a18f46e9e"
-  integrity sha512-okxYy3mxUkekM0RNjkBg8OPuzpnD2yXMAdnGOaQPSJ2wzBdE9R9pkTV+tzPZ65ORK7b57YUc6s+gROA4+EIOLg==
-  dependencies:
-    async.queue "^0.5.2"
-
 gulp-rename@^2.0.0:
   version "2.0.0"
   resolved "https://registry.yarnpkg.com/gulp-rename/-/gulp-rename-2.0.0.tgz#9bbc3962b0c0f52fc67cd5eaff6c223ec5b9cf6c"