cranelift: Remove is_pic predicate from x86 backend (#5548)

This is still present as shared flags and we don't use the predicate anywhere.

cranelift/codegen/meta/src/cdsl/settings.rs

@@ -181,7 +181,6 @@ struct ProtoSetting {
 pub(crate) enum PredicateNode {
     OwnedBool(BoolSettingIndex),
     SharedBool(&'static str, &'static str),
-    Not(Box<PredicateNode>),
     And(Box<PredicateNode>, Box<PredicateNode>),
 }
 
@@ -211,7 +210,6 @@ impl PredicateNode {
             PredicateNode::And(ref lhs, ref rhs) => {
                 format!("{} && {}", lhs.render(group), rhs.render(group))
             }
-            PredicateNode::Not(ref node) => format!("!({})", node.render(group)),
         }
     }
 }