Remove online migration feature from 3.0.9 and 3.1.5 release notes

This was incorrectly copy and pasted from the 2.16.19 release
notes.

Change-Id: I8fdda32c88646ee45a07361386fa42550f95dc81
diff --git a/pages/site/releases/3.0.md b/pages/site/releases/3.0.md
index 8cd41b6..2745893 100644
--- a/pages/site/releases/3.0.md
+++ b/pages/site/releases/3.0.md
@@ -198,15 +198,6 @@
 
 * New Features
 
-  * Enable to run online noteDb migration using multiple threads.
-
-    The new configuration option
-    [`notedb.onlineMigrationThreads`](http://gerrit-documentation.storage.googleapis.com/Documentation/3.0.9/config-gerrit.html#notedb.onlineMigrationThreads)
-    allows tuning the number of threads the migration can use.
-
-    This helps to speed up online migration at the expense of imposing a
-    higher load on the Gerrit server running at the same time.
-
   * Add a new metric for monitoring Java deadlocks.
 
     The metric `proc/jvm/thread/num_deadlocked_threads` monitors the number of
diff --git a/pages/site/releases/3.1.md b/pages/site/releases/3.1.md
index 3511ef7..2d83f9d 100644
--- a/pages/site/releases/3.1.md
+++ b/pages/site/releases/3.1.md
@@ -298,15 +298,6 @@
 
 * New Features
 
-  * Enable to run online noteDb migration using multiple threads.
-
-    The new configuration option
-    [`notedb.onlineMigrationThreads`](http://gerrit-documentation.storage.googleapis.com/Documentation/3.1.5/config-gerrit.html#notedb.onlineMigrationThreads)
-    allows tuning the number of threads the migration can use.
-
-    This helps to speed up online migration at the expense of imposing a
-    higher load on the Gerrit server running at the same time.
-
   * Add a new metric for monitoring Java deadlocks.
 
     The metric `proc/jvm/thread/num_deadlocked_threads` monitors the number of