Cleanup: Remove misplaced config.h include

config.h should _always_ be included first, before system headers, to
ensure coherent size_t across the file.

We force the config.h inclusion by the compiler, so this is not an issue
(configure.ac: DEFAULT_INCLUDES="-I\$(top_srcdir) -I\$(top_builddir)
-I\$(top_builddir)/src -I\$(top_builddir)/include -include config.h"),
but let's remove this misleading line of code.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>