fix(dashboard): Minor cleanup and improve text legibility (#7045)

**What**
- Cleans up some artifacts from the V1 -> V2 migrations.
- Removes the MedusaProvider from the root in favor of a plain QueryClient.
- Applies font styles to make the text in admin resemble designs in Figma more closely.

packages/admin-next/dashboard/src/lib/debounce.ts

@@ -1,20 +0,0 @@
-type Options = {
-  leading?: boolean
-}
-
-export const debounce = (
-  func: (...args: any[]) => void,
-  delay: number,
-  { leading }: Options = {}
-): ((...args: any[]) => void) => {
-  let timerId: NodeJS.Timeout | undefined
-
-  return (...args) => {
-    if (!timerId && leading) {
-      func(...args)
-    }
-    clearTimeout(timerId)
-
-    timerId = setTimeout(() => func(...args), delay)
-  }
-}

packages/admin-next/dashboard/src/lib/uppercase-first.ts

@@ -1,4 +0,0 @@
-export function upperCaseFirst(str: string): string {
-    return str.charAt(0).toUpperCase() + str.slice(1)
-  }
-