Remove double transpose flag in MHA fusion (#2483)

The double_transpose option to control the MHA fusion is no longer used
(with recent simplifications). Remove this flag. (Overlooked this in the
recent PR.)

Signed-off-by: Ganesan Ramalingam <[email protected]>

Author: gramalingam

onnxscript/rewriter/ort_fusions/mha.py

@@ -37,13 +37,11 @@ def __init__(
         self,
         name,
         *,
-        double_transpose: bool,
         is_rotary: bool,
         has_past_present: bool,
         is_cross_attention: bool,
     ):
         super().__init__(name)
-        self._double_transpose = double_transpose
         self._is_rotary = is_rotary
         self._has_past_present = has_past_present
         self._is_cross_attention = is_cross_attention
@@ -345,12 +343,10 @@ def rewrite(
 def _make_rule_set(has_past_present: bool):
     parameter_combinations = [
         {
-            "double_transpose": double_transpose,
             "is_rotary": is_rotary,
             "has_past_present": has_past_present,
             "is_cross_attention": is_cross_attention,
         }
-        for double_transpose in [False, True]
         for is_rotary in [False, True]
         for is_cross_attention in ([False] if has_past_present else [False, True])
     ]
@@ -360,7 +356,6 @@ def _make_rule_set(has_past_present: bool):
         [
             MultiHeadAttention.rule(
                 f"MHA"
-                f"{'_Twice' if params['double_transpose'] else ''}"
                 f"{'_Rotary' if params['is_rotary'] else ''}"
                 f"{'_Past' if params['has_past_present'] else ''}"
                 f"{'_CrossAttention' if params['is_cross_attention'] else ''}",