DynamicTablesPkg: Remove duplicated words

In an effort to clean the documentation of the above
package, remove duplicated words.

Cc: Sami Mujawar <Sami.Mujawar@arm.com>
Cc: Alexei Fedorov <Alexei.Fedorov@arm.com>
Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>

DynamicTablesPkg/Library/Common/AmlLib/AmlNodeDefines.h

@@ -34,7 +34,7 @@ typedef AML_NODE_HEADER *AML_NODE_HANDLE;
 
 /** AML root node.
 
-  The root node is unique and at the head of of tree. It is a fake node used
+  The root node is unique and at the head of tree. It is a fake node used
   to maintain the list of AML statements (stored as object nodes) which are
   at the first scope level.
 */