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/Api/AmlApiHelper.h

@@ -19,7 +19,7 @@
   of NameSegs that have less that 4 chars, like "DEV". "DEV" will be expanded
   as "DEV_".
 
-  An AML NameString is not NULL terminated and is is only composed of
+  An AML NameString is not NULL terminated and is only composed of
   4 chars long NameSegs.
 
   @param  [in] NameOpNode   NameOp object node defining a variable.