test: remove leftover spdk_cunit declaration

The function itself was removed, but the declaration in the header was
left behind.

Change-Id: Idbff42c197ef56e65fa92c6795306d9326381cf9
Fixes: ca1de9eb75 ("test: remove spdk_cunit library")
Signed-off-by: Daniel Verkamp <daniel.verkamp@intel.com>
Reviewed-on: https://review.gerrithub.io/418231
Tested-by: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Jim Harris <james.r.harris@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>

test/spdk_cunit.h

@@ -53,6 +53,4 @@
 		}				\
 	} while (0)
 
-int spdk_cunit_print_results(const char *filename);
-
 #endif /* SPDK_CUNIT_H */