middle-end: Remove unused internal function after IVopts cleanup [PR118756]

It seems that after my IVopts patches the function contain_complex_addr_expr
became unused and clang is rightfully complaining about it.

This removes the unused internal function.

gcc/ChangeLog:

	PR tree-optimization/118756
	* tree-ssa-loop-ivopts.cc (contain_complex_addr_expr): Remove.