tidy: extdeps.rs: Clean up loop iteration to use "for"
tidy: extdeps.rs: Clean up loop iteration to use "for"

Also eliminates a clippy lint.

aidancully/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,aidancully/rust,aidancully/rust,GBGamer/rust,aidancully/rust,graydon/rust,GBGamer/rust,GBGamer/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,GBGamer/rust,GBGamer/rust,aidancully/rust