Clean up unused function declaration

We removed the definition a while ago, but forgot to remove the
declaration in the header.

BUG=959231

Change-Id: I6e58af7a4337df8957bb4f8c5b6b670fd9233252
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594892Reviewed-by: Joe Mason <joenotcharles@google.com>
Commit-Queue: Sean Risser <srisser@google.com>
Cr-Commit-Position: refs/heads/master@{#656437}

chrome/chrome_cleaner/os/system_util_cleaner.h

@@ -32,12 +32,6 @@ bool HasDebugRightsPrivileges();
 // @returns true if the current process is running elevated.
 bool HasAdminRights();
 
-// Check whether the thumbprint (sha1) of the signing certificate of a given
-// file is part of a sorted array of thumbprints.
-bool IsFileCertificateThumbprintInArray(const base::FilePath& fullpath,
-                                        const char* const thumbprints[],
-                                        size_t thumbprints_length);
-
 // Check whether a process is running with the image |executable|. Return true
 // if a process is found.
 bool IsProcessRunning(const wchar_t* executable);