user upgrades: update incentive descriptions.

* Call them hidden tags instead of censored tags so that users don't
  think that buying gold removes censorship from images (yes, this happened).

* Remove API ratelimit information (not relevant to most users).

app/views/user_upgrades/new.html.erb

@@ -68,23 +68,11 @@
               <td>1,000</td>
             </tr>
             <tr>
-              <td>See Censored Tags</td>
+              <td>See Hidden Tags</td>
               <td>No</td>
               <td>Yes</td>
               <td>Yes</td>
             </tr>
-            <tr>
-              <td>Max API Requests Per Second</td>
-              <td>15</td>
-              <td>30</td>
-              <td>60</td>
-            </tr>
-            <tr>
-              <td>API Regen Per Second</td>
-              <td>1</td>
-              <td>2</td>
-              <td>4</td>
-            </tr>
             <tr>
               <td>Search Timeout</td>
               <td>3 sec</td>