Get rid of operand_kind()

This method caused lots of import cycles when type checking.

Use isinstance() in the Operand constructor instead to decipher the
OperandSpec union type.

lib/cretonne/meta/cdsl/operands.py

@@ -32,14 +32,6 @@ class OperandKind(object):
         # type: () -> str
         return 'OperandKind({})'.format(self.name)
 
-    def operand_kind(self):
-        # type: () -> OperandKind
-        """
-        An `OperandKind` instance can be used directly as the type of an
-        `Operand` when defining an instruction.
-        """
-        return self
-
     def free_typevar(self):
         # Return the free typevariable controlling the type of this operand.
         return None

lib/cretonne/meta/cdsl/typevar.py

@@ -6,7 +6,6 @@ polymorphic by using type variables.
 """
 from __future__ import absolute_import
 import math
-import cdsl.operands
 
 try:
     from typing import Tuple, Union # noqa
@@ -314,13 +313,6 @@ class TypeVar(object):
 
         return TypeVar(None, None, base=self, derived_func='DoubleWidth')
 
-    def operand_kind(self):
-        # type: () -> cdsl.operands.OperandKind
-        # When a `TypeVar` object is used to describe the type of an `Operand`
-        # in an instruction definition, the kind of that operand is an SSA
-        # value.
-        return cdsl.operands.VALUE
-
     def free_typevar(self):
         # type: () -> TypeVar
         if self.is_derived: