This reverts commit a333d6a8.

The change did not resolve the test issue in travis.

Closes https://github.com/cython/cython/issues/3775

This is a follow up to https://github.com/cython/cython/pull/3307

Closes https://github.com/cython/cython/pull/3763

Use NumPy 1.18.x for testing on travis as long as 1.19.[01+] ships a numpy.pxd that is incompatible with Cython 3.0.

Try to fix NumPy test failures by not setting the "NPY_NO_DEPRECATED_API" #define for NumPy 1.19.[01].

Change "Py_intptr_t" declaration in numpy.pxd to what CPython uses as fallback. "int" seems overly lazy if it tends to be larger on many systems.