Rollup merge of #35917 - jseyfried:remove_attr_ext_traits, r=nrc

syntax: Remove traits `AttrMetaMethods`, `AttributeMethods`, and `AttrNestedMetaItemMethods`

src/libsyntax/print/pprust.rs

@@ -16,7 +16,6 @@ use ast::{SelfKind, RegionTyParamBound, TraitTyParamBound, TraitBoundModifier};
 use ast::Attribute;
 use util::parser::AssocOp;
 use attr;
-use attr::{AttrMetaMethods, AttributeMethods};
 use codemap::{self, CodeMap};
 use syntax_pos::{self, BytePos};
 use errors;