Move rustc_middle::limits to rustc_interface.

It's always good to make `rustc_middle` smaller. `rustc_interface` is
the best destination, because it's the only crate that calls
`get_recursive_limit`.

compiler/rustc_middle/src/error.rs

@@ -67,16 +67,6 @@ pub enum TypeMismatchReason {
     },
 }
 
-#[derive(Diagnostic)]
-#[diag(middle_limit_invalid)]
-pub(crate) struct LimitInvalid<'a> {
-    #[primary_span]
-    pub span: Span,
-    #[label]
-    pub value_span: Span,
-    pub error_str: &'a str,
-}
-
 #[derive(Diagnostic)]
 #[diag(middle_recursion_limit_reached)]
 #[help]