pybind: remove compile_time_env parameter from setup.py files

pybind: remove compile_time_env parameter from setup.py files

Cython's IF statement for conditional compilation has been deprecated
in Cython 3.0 as documented at:
https://cython.readthedocs.io/en/latest/src/userguide/migrating_to_cy30.html#deprecation-of-def-if

The compile_time_env parameter was used to pass compile-time constants
(BUILD_DOC and UNAME_SYSNAME) to Cython's IF statements. Since we have
migrated away from Cython's IF statements, this parameter is no longer
needed:

- Platform-specific code now uses C preprocessor conditionals (#if
  defined(__FreeBSD__)) directly in cdef extern blocks
- BUILD_DOC conditionals are handled via Tempita template processing
  for .pyx files, not Cython's compile-time IF statements

Remove the compile_time_env parameter from all pybind setup.py files
(cephfs, rados, rbd, rgw) as it serves no purpose after the migration
to Cython 3.0-compatible approaches.

Also, take this opportunity to completely drop `compiler_directives`
which should have been removed in 0423b771.

Signed-off-by: Kefu Chai <k.chai@proxmox.com>