fix: revert change that caused headers to be double merged if provider was authed in multiple places (#12072)

packages/opencode/src/provider/provider.ts

@@ -987,12 +987,6 @@ export namespace Provider {
         const fetchFn = customFetch ?? fetch
         const opts = init ?? {}
 
-        // Merge configured headers into request headers
-        opts.headers = {
-          ...(opts.headers ?? {}),
-          ...options["headers"],
-        }
-
         if (options["timeout"] !== undefined && options["timeout"] !== null) {
           const signals: AbortSignal[] = []
           if (opts.signal) signals.push(opts.signal)