Corrected synopsis part for 'apt-get' source.

doc/apt-get.8.xml

@@ -76,11 +76,9 @@
          <arg>purge <arg choice="plain" rep="repeat"><replaceable>pkg</replaceable></arg></arg>
          <arg>source 
 			 <arg choice="plain" rep="repeat"><replaceable>pkg</replaceable>
-				 <group choice='opt'>
-					 <arg>
-						 =<replaceable>pkg_version_number</replaceable>
-					 </arg>
-				 </group>
+				 <arg>
+					 =<replaceable>pkg_version_number</replaceable>
+				 </arg>
 			 </arg>
 	     </arg>
          <arg>build-dep <arg choice="plain" rep="repeat"><replaceable>pkg</replaceable></arg></arg>