Drop stale @available attributes from context-provider witnesses

Xcode 26.4.1 tightened protocol-witness availability rules: when one
class satisfies both ASWebAuthenticationPresentationContextProviding
(iOS 12+) and ASAuthorizationControllerPresentationContextProviding
(iOS 13+), the shared 'presentationAnchor(for:)' witnesses must be as
available as the least-restrictive protocol, not their individual
availability. That produced:

  Protocol 'ASAuthorizationControllerPresentationContextProviding'
  requires 'presentationAnchor(for:)' to be available in iOS 12.0 and newer

The @available attributes were left over from when the SDK supported
older deployment targets. The SDK now ships with IPHONEOS_DEPLOYMENT_TARGET
14.2, so both ASWebAuthenticationSession and ASAuthorizationController
are unconditionally available. Drop the attributes; the compiler no
longer complains and behavior is unchanged.

Author: ssathy2

IFTTT SDK/AuthenticationSessionPresentationContextProvider.swift

@@ -21,12 +21,10 @@ class AuthenticationSessionContextPresentationProvider: NSObject, ASWebAuthentic
         super.init()
     }
 
-    @available(iOS 12.0, *)
     func presentationAnchor(for session: ASWebAuthenticationSession) -> ASPresentationAnchor {
         return presentationContext
     }
-    
-    @available(iOS 13.0, *)
+
     func presentationAnchor(for controller: ASAuthorizationController) -> ASPresentationAnchor {
         return presentationContext
     }