plpython: Avoid the need to redefine *printf macros

plpython: Avoid the need to redefine *printf macros

Until now we undefined and then redefined a lot of *printf macros due to
worries about conflicts with Python.h macro definitions. Current Python.h
doesn't define any *printf macros, and older versions just defined snprintf,
vsnprintf, guarded by #if defined(MS_WIN32) && !defined(HAVE_SNPRINTF).

Thus we can replace the undefine/define section with a single
 #define HAVE_SNPRINTF 1

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/20230124165814.2njc7gnvubn2amh6@awork3.anarazel.de