Remove non working Reindex --dry-run option

In Ic4808d1e3, --dry-run option was replaced by --output.  Icf42a3eb2
brought back the option declaration but not the code so the option is
not working.

Change-Id: Ic945a64f6184c15f84fe998e754046fae390b0f7
diff --git a/gerrit-pgm/src/main/java/com/google/gerrit/pgm/Reindex.java b/gerrit-pgm/src/main/java/com/google/gerrit/pgm/Reindex.java
index 5bedfe3..00914d2 100644
--- a/gerrit-pgm/src/main/java/com/google/gerrit/pgm/Reindex.java
+++ b/gerrit-pgm/src/main/java/com/google/gerrit/pgm/Reindex.java
@@ -63,9 +63,6 @@
   @Option(name = "--verbose", usage = "Output debug information for each change")
   private boolean verbose;
 
-  @Option(name = "--dry-run", usage = "Dry run: don't write anything to index")
-  private boolean dryRun;
-
   private Injector dbInjector;
   private Injector sysInjector;
   private Config globalConfig;