Remove a reference to Valgrind in DiskCacheBackendTest.

Valgrind bots are gone.

BUG=605605

Change-Id: Ie722b831d0a6fca8b48620e5a9d993896346cbef
Reviewed-on: https://chromium-review.googlesource.com/1014956Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#551376}

net/disk_cache/backend_unittest.cc

@@ -802,9 +802,6 @@ TEST_F(DiskCacheBackendTest, ShutdownWithPendingFileIO) {
 
 // Here and below, tests that simulate crashes are not compiled in LeakSanitizer
 // builds because they contain a lot of intentional memory leaks.
-// The wrapper scripts used to run tests under Valgrind Memcheck will also
-// disable these tests. See:
-// tools/valgrind/gtest_exclude/net_unittests.gtest-memcheck.txt
 #if !defined(LEAK_SANITIZER)
 // We'll be leaking from this test.
 TEST_F(DiskCacheBackendTest, ShutdownWithPendingFileIO_Fast) {