Remove the vconst instruction and the UnaryImmVector format.

No instruction sets actually have single instructions for materializing
vector constants. You always need to use a constant pool.

Cretonne doesn't have constant pools yet, but it will in the future, and
that is how vector constants should be represented.

lib/cretonne/meta/base/instructions.py

@@ -9,7 +9,7 @@ from cdsl.operands import Operand, VARIABLE_ARGS
 from cdsl.typevar import TypeVar
 from cdsl.instructions import Instruction, InstructionGroup
 from base.types import i8, f32, f64, b1
-from base.immediates import imm64, uimm8, ieee32, ieee64, immvector
+from base.immediates import imm64, uimm8, ieee32, ieee64
 from base.immediates import intcc, floatcc
 from base import entities
 import base.formats  # noqa
@@ -196,16 +196,6 @@ f64const = Instruction(
         """,
         ins=N, outs=a)
 
-N = Operand('N', immvector)
-a = Operand('a', TxN, doc='A constant vector value')
-vconst = Instruction(
-        'vconst', r"""
-        Vector constant (floating point or integer).
-
-        Create a SIMD vector value where the lanes don't have to be identical.
-        """,
-        ins=N, outs=a)
-
 #
 # Generics.
 #