unbreak graphics/pdf2djvu with poppler-20.x

Hi,

looks like the poppler people decided that their API is now stable,
and replaced POPPLER_VERSION with what was formerly known as
POPPLER_VERSION_STRING. Starting with poppler-20.x, poppler-config.h
defines POPPLER_VERSION like this:

#define POPPLER_VERSION "20.09.0"

Of course, this breaks all the #if POPPLER_VERSION < 666, so I just
patched out all those preprocessor conditionals.

No intended package change, so no bump.

ok?

Ciao,
Kili

ps: while waiting for my partial bulk to finish, i expect more
fallout similar to this shit.

Index: patches/patch-pdf-backend_cc
===================================================================
RCS file: patches/patch-pdf-backend_cc
diff -N patches/patch-pdf-backend_cc
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ patches/patch-pdf-backend_cc 3 Sep 2020 20:38:55 -0000
@@ -0,0 +1,98 @@
+$OpenBSD$
+
+Starting with poppler-20, POPPLER_VERSION no longer is numeric -- it's
+what POPPLER_VERSION_STRING was in earlier releases.
+
+Index: pdf-backend.cc
+--- pdf-backend.cc.orig
++++ pdf-backend.cc
+@@ -48,11 +48,7 @@
+ * ======================
+ */
+
+-#if POPPLER_VERSION >= 8500
+ static void poppler_error_handler(ErrorCategory category, pdf::Offset pos, const char *message)
+-#else
+-static void poppler_error_handler(void *data, ErrorCategory category, pdf::Offset pos, const char *message)
+-