Remove use of CRATES_IO_INDEX in cargo-test-support.
Remove use of CRATES_IO_INDEX in cargo-test-support.

Unfortunate duplication of the string, but I think it is unlikely
to have any consequences.

nipunn1313/cargo,eminence/cargo,eminence/cargo,rust-lang/cargo,rustyhorde/cargo,nipunn1313/cargo,eminence/cargo,rust-lang/cargo,nipunn1313/cargo,rust-lang/cargo,rustyhorde/cargo,nipunn1313/cargo,rustyhorde/cargo,rust-lang/cargo,eminence/cargo,rustyhorde/cargo