chore(gatsby): remove @types/webpack-merge

webpack-merge now ships its own type definitions as of v5

Author: hoobdeebla

package.json

@@ -27,7 +27,6 @@
     "@types/signal-exit": "^3.0.0",
     "@types/stack-trace": "^0.0.29",
     "@types/webpack": "^4.41.18",
-    "@types/webpack-merge": "^4.1.5",
     "@typescript-eslint/eslint-plugin": "^2.24.0",
     "@typescript-eslint/parser": "^2.24.0",
     "babel-eslint": "^10.1.0",

yarn.lock

@@ -4025,13 +4025,6 @@
     "@types/webpack" "*"
     loglevel "^1.6.2"
 
-"@types/webpack-merge@^4.1.5":
-  version "4.1.5"
-  resolved "https://registry.yarnpkg.com/@types/webpack-merge/-/webpack-merge-4.1.5.tgz#265fbee4810474860d0f4c17e0107032881eed47"
-  integrity sha512-cbDo592ljSHeaVe5Q39JKN6Z4vMhmo4+C3JbksOIg+kjhKQYN2keGN7dvr/i18+dughij98Qrsfn1mU9NgVoCA==
-  dependencies:
-    "@types/webpack" "*"
-
 "@types/webpack-sources@*":
   version "0.1.5"
   resolved "https://registry.yarnpkg.com/@types/webpack-sources/-/webpack-sources-0.1.5.tgz#be47c10f783d3d6efe1471ff7f042611bd464a92"