Remove redundant tests

Issues in those parts will likely be caught by other parts of the test suite.

Author: Kyuuhachi

tests/rustdoc/issue-118180-empty-tuple-struct.rs

@@ -2,18 +2,8 @@
 pub enum Enum {
     // @has - '//*[@id="variant.Empty"]//h3' 'Empty()'
     Empty(),
-    // @has - '//*[@id="variant.Hidden"]//h3' 'Hidden(/* private fields */)'
-    Hidden(#[doc(hidden)] u8),
 }
 
 // @has issue_118180_empty_tuple_struct/struct.Empty.html
 // @has - '//pre/code' 'Empty()'
 pub struct Empty();
-
-// @has issue_118180_empty_tuple_struct/struct.Hidden.html
-// @has - '//pre/code' 'Hidden(/* private fields */)'
-pub struct Hidden(#[doc(hidden)] pub u8);
-
-// @has issue_118180_empty_tuple_struct/struct.Private.html
-// @has - '//pre/code' 'Private(/* private fields */)'
-pub struct Private(());