Auto merge of #62099 - Mark-Simulacrum:syntax-print-clean-2, r=eddyb

Remove io::Result from syntax::print

Since we're now writing directly to the vector, there's no need to
thread results through the whole printing infrastructure

diff --cc src/librustc/hir/map/mod.rs
Simple merge

diff --cc src/librustc/hir/print.rs
Simple merge

diff --cc src/librustc_borrowck/dataflow.rs
Simple merge

diff --cc src/librustc_driver/pretty.rs
Simple merge

diff --cc src/libsyntax/parse/parser.rs
Simple merge

diff --cc src/libsyntax/test.rs
Simple merge