Remove ParseSess methods that duplicate DiagCtxt methods.

Also add missing `#[track_caller]` attributes to `DiagCtxt` methods as
necessary to keep tests working.

compiler/rustc_builtin_macros/src/asm.rs

@@ -422,7 +422,7 @@ fn parse_reg<'a>(
             ast::InlineAsmRegOrRegClass::Reg(symbol)
         }
         _ => {
-            return Err(p.sess.create_err(errors::ExpectedRegisterClassOrExplicitRegister {
+            return Err(p.dcx().create_err(errors::ExpectedRegisterClassOrExplicitRegister {
                 span: p.token.span,
             }));
         }