Revert "Add success64_noargs helper function"

This reverts commit 4c8c7d2cdfd4eb8bc88469b59d12769aadcb4cb5.

According to FF-A spec the FFA_SUCCESS64 function ID should be used only
if any result register encodes a 64-bit parameter.

Signed-off-by: Balint Dobszay <balint.dobszay@arm.com>
Change-Id: I40efad38f5b5ccef14452370df548de03a447ab6
diff --git a/src/lib.rs b/src/lib.rs
index bfba56f..162c109 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -2337,14 +2337,6 @@
         }
     }
 
-    /// Helper function to create an `FFA_SUCCESS` interface without any arguments.
-    pub fn success64_noargs() -> Self {
-        Self::Success {
-            target_info: 0,
-            args: SuccessArgs::Args64([0; 6]),
-        }
-    }
-
     /// Helper function to create an `FFA_ERROR` interface with an error code.
     pub fn error(error_code: FfaError) -> Self {
         Self::Error {