gh-61103: don't use C _Complex types to implement F/D/G in ctypes (GH-133237)

According to the C standard, the memory representation of _Complex types
is equivalent to 2-element arrays. Unlike _Complex, arrays are always available.

- drop _complex.h header
- use appropriate real arrays to replace complex types

Co-authored-by: Lisandro Dalcin <dalcinl@gmail.com>
Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>