build: fix "make rpm"

make rpm was failing with the following error:

Entering directory `/home/laine/devel/libvirt/tests'
make[2]: *** No rule to make target `viratomicdata.h',
             needed by `distdir'.  Stop.

viratomicdata.h is listed in tests/Makefile.am as a dependency of
viratomictest, but doesn't exist, is never referenced, and removing
that dependency permits make rpm to complete successfully.

tests/Makefile.am

@@ -531,7 +531,7 @@ virhashtest_SOURCES = \
 virhashtest_LDADD = $(LDADDS)
 
 viratomictest_SOURCES = \
-	viratomictest.c viratomicdata.h testutils.h testutils.c
+	viratomictest.c testutils.h testutils.c
 viratomictest_LDADD = $(LDADDS)
 
 jsontest_SOURCES = \