Revert "Run Documentation formatting in parallel"

This reverts commit db4e14f1a8d0a0aa0b4b39ac74242ac0962e7f47.
Running AsciiDoc in parallel swamps some hardware, and there
is no portable way to get the number of available cores.

Since it is apparent the contributors want to keep using
Maven, lets just go with correct and slow.

Change-Id: I71c2c902dc1553b0316c21aaf48b481ffe0aaec6
diff --git a/gerrit-war/pom.xml b/gerrit-war/pom.xml
index a71d28b..71ed71e 100644
--- a/gerrit-war/pom.xml
+++ b/gerrit-war/pom.xml
@@ -251,7 +251,6 @@
                   <arg value="VERSION=${project.version}" />
                   <arg value="clean" />
                   <arg value="all" />
-                  <arg value="-j8" />
                 </exec>
 
                 <mkdir dir="${dst}" />
@@ -279,7 +278,6 @@
                   <arg value="VERSION=${project.version}" />
                   <arg value="clean" />
                   <arg value="all" />
-                  <arg value="-j8" />
                 </exec>
 
                 <mkdir dir="${dst}" />