cmd/vet/all: remove cmd/compile/internal/big special case

It no longer exists as of CL 31010.

Change-Id: Idd61f392544cad8b3f3f8d984dc5c953b473e2e5
Reviewed-on: https://go-review.googlesource.com/31934
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/vet/all/main.go

@@ -177,9 +177,6 @@ var ignorePathPrefixes = [...]string{
 	"cmd/go/testdata/",
 	"cmd/vet/testdata/",
 	"go/printer/testdata/",
-	// cmd/compile/internal/big is a vendored copy of math/big.
-	// Ignore it so that we only have to deal with math/big issues once.
-	"cmd/compile/internal/big/",
 }
 
 func vetPlatforms(pp []platform) {