Revert "cmd/vet/all: remove pprof from the whitelist"

This reverts commit 12b6c181.

Reason for revert: Broke vet builder. #19322 was not fully fixed.

Change-Id: Id85131d4d0b8915480d65e3532da62b769463d70
Reviewed-on: https://go-review.googlesource.com/37625Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/cmd/vet/all/main.go

@@ -191,6 +191,9 @@ var ignorePathPrefixes = [...]string{
 	// TODO: If vet ever uses go/loader and starts working off source,
 	// this problem will likely go away.
 	"fmt/fmt_test.go",
+	// Ignore pprof for the moment to get the builders happy.
+	// TODO: Fix all the issues and reinstate.
+	"cmd/vendor/github.com/google/pprof",
 }
 
 func vetPlatforms(pp []platform) {