t/unit-tests/lib-reftable.h: don't include "git-compat-util.h" twice

lib-reftable.h includes "git-compat-utils.h" not once but twice,
although it's not one of those blessed special header files that
should do so, and all source files including it do start with
including "unit-test.h", which in turn starts with including
"git-compat-util.h".

So remove the #include "git-compat-util.h" directives from this header
file.

Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com>

Author: szeder

t/unit-tests/lib-reftable.h

@@ -1,7 +1,5 @@
-#include "git-compat-util.h"
 #include "clar/clar.h"
 #include "clar-decls.h"
-#include "git-compat-util.h"
 #include "reftable/reftable-writer.h"
 #include "strbuf.h"