[MLIR] Remove unnecessary include from MathToEmitC.h to fix build issue (#125466)
This removes the unnecessary inclusion of mlir/Dialect/EmitC/IR/EmitC.h
from MathToEmitC.h, which caused a build failure due to a missing
EmitCEnums.h.inc. The include was not needed, and removing it resolves
the issue without requiring additional dependencies.