Removed typescript declaration build step for i18n (#17023)

ref https://ghost.slack.com/archives/C02G9E68C/p1686735066587639

### <samp>🤖 Generated by Copilot at f9ec3e9</samp>

This pull request removes redundant build scripts from the `ghost/i18n`
and `ghost/signup-form` packages. This simplifies the build process and
avoids unnecessary TypeScript compilation.

ghost/i18n/package.json

@@ -8,7 +8,6 @@
   "types": "./build/i18n.d.ts",
   "scripts": {
     "dev": "echo \"Implement me!\"",
-    "build": "tsc",
     "test:unit:base": "NODE_ENV=testing c8 --include index.js --include lib --check-coverage --100  --reporter text --reporter cobertura mocha './test/**/*.test.js'",
     "test:unit": "yarn test:unit:base && yarn translate",
     "test": "yarn test:unit",

ghost/i18n/tsconfig.json

@@ -1,13 +0,0 @@
-{
-    "compilerOptions": {
-      "allowJs": true,
-      "declaration": true,
-      "emitDeclarationOnly": true,
-      "outDir": "./build",
-      "skipLibCheck": true,
-      "esModuleInterop": true,
-      "allowSyntheticDefaultImports": true,
-    },
-    "include": ["lib/**/*.js"],
-    "exclude": ["node_modules", "test"]
-  }

ghost/signup-form/package.json

@@ -21,7 +21,6 @@
         "preview": "concurrently \"vite preview -l silent\" \"vite build --watch\"",
         "dev:test": "vite build && vite preview --port 6175",
         "build": "tsc && vite build",
-        "prebuild": "yarn workspace @tryghost/i18n build",
         "lint": "yarn run lint:js",
         "lint:js": "eslint --ext .js,.ts,.cjs,.tsx --cache src test",
         "test:unit": "yarn build",

ghost/signup-form/src/i18n.d.ts

@@ -0,0 +1 @@
+declare module '@tryghost/i18n';