BUG: special: remove redundant Py_Initialize

[mattip]

Reference issue

Closes #20783

What does this implement/fix?

The use of Py_Initialize in SpecFun_Initialize is redundant. This function is called in two places, both are the initialization functions called at module import time (thus the use of PyMODINIT_FUNC). Python must have been initialized for the import function to be called. What is more: PyPy does not implement Py_Initialize, so including it here needlessly breaks building SciPy on PyPy.

Additional information

Here are the calls to SpecFun_Initialize:

scipy/scipy/special/_gufuncs.cpp

Lines 61 to 63 in cdc251d

	PyMODINIT_FUNC PyInit__gufuncs() {
	if (!SpecFun_Initialize()) {
	return nullptr;

scipy/scipy/special/_special_ufuncs.cpp

Lines 214 to 216 in cdc251d

	PyMODINIT_FUNC PyInit__special_ufuncs() {
	if (!SpecFun_Initialize()) {
	return nullptr;

[lucascolley]

thanks @mattip !