Remove stale TODO.

In non-NaCl builds, we've since replaced that file with a call to
BoringSSL's SHA-1, which we ship regardless.

Bug: 47218
Change-Id: Ie61f21378fe00566a218f42a8a3ecd7832eb46f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1827385
Commit-Queue: David Benjamin <davidben@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Auto-Submit: David Benjamin <davidben@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700481}

base/hash/sha1.cc

@@ -29,10 +29,6 @@ namespace base {
 //
 // to reuse the instance of sha, call sha.Init();
 
-// TODO(jhawkins): Replace this implementation with a per-platform
-// implementation using each platform's crypto library.  See
-// http://crbug.com/47218
-
 class SecureHashAlgorithm {
  public:
   SecureHashAlgorithm() { Init(); }