Change 'print(fmt!(...))' to printf!/printfln! in src/lib*
Change 'print(fmt!(...))' to printf!/printfln! in src/test/
auto merge of #7968 : poiru/rust/print-fmt-cleanup, r=brson

This changes `print(fmt!(...))` and `println(fmt!(...))` to `printf!(...)` and `printfln!(...)`. I also removed the format specifier in places where it was `"%?"`. Others specifiers, such as `"%s"` can be removed, too, but perhaps those are best left for another PR.