[Vertex AI] Remove supported platforms #warning (#13738)

Author: andrewheard

FirebaseVertexAI/Sources/Constants.swift

@@ -14,10 +14,6 @@
 
 import Foundation
 
-#if !os(macOS) && !os(iOS)
-  #warning("Only iOS, macOS, and Catalyst targets are currently fully supported.")
-#endif
-
 /// Constants associated with the Vertex AI for Firebase SDK.
 enum Constants {
   /// The Vertex AI backend endpoint URL.