Standardize SSH key storage

Summary:
Ref T5833. This fixes a few weird things with this table:

  - A bunch of columns were nullable for no reason.
  - We stored an MD5 hash of the key (unusual) but never used it and callers were responsible for manually populating it.
  - We didn't perform known-key-text lookups by using an index.

Test Plan:
  - Ran migrations.
  - Faked duplicate keys, saw them clean up correctly.
  - Added new keys.
  - Generated new keys.
  - Used `bin/auth-ssh` and `bin/auth-ssh-key`.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5833

Differential Revision: https://secure.phabricator.com/D10805

src/applications/auth/query/PhabricatorAuthSSHKeyQuery.php

@@ -73,21 +73,18 @@ final class PhabricatorAuthSSHKeyQuery
     if ($this->objectPHIDs !== null) {
       $where[] = qsprintf(
         $conn_r,
-        'userPHID IN (%Ls)',
+        'objectPHID IN (%Ls)',
         $this->objectPHIDs);
     }
 
     if ($this->keys !== null) {
-      // TODO: This could take advantage of a better key, and the hashing
-      // scheme for this table is a bit nonstandard and questionable.
-
       $sql = array();
       foreach ($this->keys as $key) {
         $sql[] = qsprintf(
           $conn_r,
-          '(keyType = %s AND keyBody = %s)',
+          '(keyType = %s AND keyIndex = %s)',
           $key->getType(),
-          $key->getBody());
+          $key->getHash());
       }
       $where[] = implode(' OR ', $sql);
     }