Cranelift: Remove ifcmp_sp opcode. (#4578)

This was temporarily added back in #3502 due to a need from Lucet; now
that Lucet is EOL, the opcode is no longer needed and we can remove it.

cranelift/codegen/meta/src/shared/instructions.rs

@@ -1590,21 +1590,6 @@ pub(crate) fn define(
         .operands_out(vec![a]),
     );
 
-    ig.push(
-        Inst::new(
-            "ifcmp_sp",
-            r#"
-    Compare ``addr`` with the stack pointer and set the CPU flags.
-
-    This is like `ifcmp` where ``addr`` is the LHS operand and the stack
-    pointer is the RHS.
-    "#,
-            &formats.unary,
-        )
-        .operands_in(vec![addr])
-        .operands_out(vec![flags]),
-    );
-
     let x = &Operand::new("x", TxN).with_doc("Vector to split");
     let lo = &Operand::new("lo", &TxN.half_vector()).with_doc("Low-numbered lanes of `x`");
     let hi = &Operand::new("hi", &TxN.half_vector()).with_doc("High-numbered lanes of `x`");