Fix HIR printing of existential type rust-lang#60662

This fixes rust-lang#60662

src/librustc/hir/print.rs

@@ -646,7 +646,6 @@ impl<'a> State<'a> {
 
                 self.print_where_clause(&exist.generics.where_clause)?;
                 self.s.space()?;
-                self.word_space(":")?;
                 let mut real_bounds = Vec::with_capacity(exist.bounds.len());
                 for b in exist.bounds.iter() {
                     if let GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = *b {

src/test/ui/issues/issue-60662.rs

@@ -0,0 +1,11 @@
+// compile-pass
+// compile-flags: -Z unpretty=hir
+
+#![feature(existential_type)]
+
+trait Animal {
+}
+
+fn main() {
+    pub existential type ServeFut: Animal;
+}

src/test/ui/issues/issue-60662.stdout

@@ -0,0 +1,14 @@
+// compile-pass
+// compile-flags: -Z unpretty=hir
+
+#![feature(existential_type)]
+#[prelude_import]
+use ::std::prelude::v1::*;
+#[macro_use]
+extern crate std;
+
+trait Animal { }
+
+fn main() {
+              pub existential type ServeFut : Animal;
+          }