Delete unused import statement for Executorch TOSA dialect (#12269)

### Summary
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Author: psiddh

backends/arm/_passes/arm_pass_manager.py

@@ -6,8 +6,6 @@
 # LICENSE file in the root directory of this source tree.
 
 # pyre-unsafe
-
-import executorch.backends.arm.tosa.dialect  # noqa: unused
 from executorch.backends.arm._passes import (
     AddBiasPass,
     AnnotateChannelsLastDimOrder,