Remove gmpy workaround

pystencils/__init__.py

 """Module to generate stencil kernels in C or CUDA using sympy expressions and call them as Python functions"""
-from . import sympy_gmpy_bug_workaround  # NOQA
 from . import fd
 from . import stencil as stencil
 from .assignment import Assignment, assignment_from_stencil

pystencils/session.py

@@ -4,6 +4,5 @@ import sympy as sp
 import pystencils as ps
 import pystencils.jupyter
 import pystencils.plot as plt
-import pystencils.sympy_gmpy_bug_workaround
 
 __all__ = ['sp', 'np', 'ps', 'plt']

pystencils/sympy_gmpy_bug_workaround.py

-# Disable gmpy backend until this bug is resolved if joblib serialize
-# See https://github.com/sympy/sympy/pull/13530
-import os
-import warnings
-
-os.environ['MPMATH_NOGMPY'] = '1'
-try:
-    import mpmath.libmp
-    # In case the user has imported sympy first, then pystencils
-    if mpmath.libmp.BACKEND == 'gmpy':
-        warnings.warn("You are using the gmpy backend. You might encounter an error 'argument is not an mpz sympy'. "
-                      "This is due to a known bug in sympy/gmpy library. "
-                      "To prevent this, import pystencils first then sympy or set the environment variable "
-                      "MPMATH_NOGMPY=1")
-except ImportError:
-    pass
-
-__all__ = []