Remove the unused anon_num_here error.

Author: nnethercote

compiler/rustc_infer/messages.ftl

@@ -163,7 +163,6 @@ infer_region_explanation = {$pref_kind ->
     [as_defined] the lifetime `{$desc_arg}` as defined here
     [as_defined_anon] the anonymous lifetime as defined here
     [defined_here] the anonymous lifetime defined here
-    [anon_num_here] the anonymous lifetime #{$desc_num_arg} defined here
     [defined_here_reg] the lifetime `{$desc_arg}` as defined here
 }{$suff_kind ->
     *[should_not_happen] [{$suff_kind}]

compiler/rustc_infer/src/errors/note_and_explain.rs

@@ -9,7 +9,6 @@ struct DescriptionCtx<'a> {
     span: Option<Span>,
     kind: &'a str,
     arg: String,
-    num_arg: u32,
 }
 
 impl<'a> DescriptionCtx<'a> {
@@ -113,7 +112,6 @@ impl<'a> DescriptionCtx<'a> {
     fn add_to(self, diag: &mut rustc_errors::Diagnostic) {
         diag.set_arg("desc_kind", self.kind);
         diag.set_arg("desc_arg", self.arg);
-        diag.set_arg("desc_num_arg", self.num_arg);
     }
 }