Remove Function::is_call

The documentation says that this is only used for heuristics, but it
is never actually called. This should be removed for now and perhaps
added back later if we find an actual use for it.

src/fuzzing/func.rs

@@ -15,7 +15,6 @@ use arbitrary::{Arbitrary, Unstructured};
 pub enum InstOpcode {
     Phi,
     Op,
-    Call,
     Ret,
     Branch,
 }
@@ -104,10 +103,6 @@ impl Function for Func {
         &self.block_params[block.index()][..]
     }
 
-    fn is_call(&self, insn: Inst) -> bool {
-        self.insts[insn.index()].op == InstOpcode::Call
-    }
-
     fn is_ret(&self, insn: Inst) -> bool {
         self.insts[insn.index()].op == InstOpcode::Ret
     }
@@ -500,11 +495,10 @@ impl Func {
                         .all(|op| !builder.f.reftype_vregs.contains(&op.vreg()))
                     && bool::arbitrary(u)?;
 
-                let op = *u.choose(&[InstOpcode::Op, InstOpcode::Call])?;
                 builder.add_inst(
                     Block::new(block),
                     InstData {
-                        op,
+                        op: InstOpcode::Op,
                         operands,
                         clobbers,
                         is_safepoint,