Remove remaining unnecessary delta from upstream

Upstream applied a slightly different fix to the Doxygen macro that
didn't require one change of quoting that our fix had.  Remove the
unnecessary delta.

doxygen.m4

@@ -79,7 +79,7 @@ AC_DEFUN([DX_IF_FEATURE], [ifelse(DX_FEATURE_$1, ON, [$2], [$3])])
 # Require the specified program to be found for the DX_CURRENT_FEATURE to work.
 AC_DEFUN([DX_REQUIRE_PROG], [
 AC_PATH_TOOL([$1], [$2])
-if test "$[DX_FLAG_]DX_CURRENT_FEATURE$$1" = 1; then
+if test "$DX_FLAG_[]DX_CURRENT_FEATURE$$1" = 1; then
     AC_MSG_WARN([$2 not found - will not DX_CURRENT_DESCRIPTION])
     AC_SUBST([DX_FLAG_]DX_CURRENT_FEATURE, 0)
 fi