starmath: Drop unused variable declaration

Change-Id: Ibc2a5930e516628cfe5fb7986c4ba814533dbf25
Reviewed-on: https://gerrit.libreoffice.org/22692Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: David Tardon <dtardon@redhat.com>

starmath/inc/node.hxx

@@ -54,8 +54,6 @@ enum class FontSizeType {
 #define FLG_HORALIGN    0x0040
 
 
-extern SmFormat *pActiveFormat;
-
 class SmVisitor;
 class SmDocShell;
 class SmNode;