Suggest removing .into() for argument that already accepts Into<_>

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When calling a method bar that takes an argument Into<Foo> with bar(foo.into()), the type system can't figure out the type for the argument. Suggest removing the .into() call.

error[E0283]: type annotations required: cannot resolve `_: std::convert::Into<syntax_pos::MultiSpan>`
  --> libsyntax_ext/concat.rs:80:26
   |
80 |         let mut err = cx.struct_span_err(
   |                          ^^^^^^^^^^^^^^^
81 |             b_pos.into(),
   |                  ------- help: remove this call

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Fixed by #121100