Remove intsettest declaration from intset.h (#471)

All the intset unit tests are migrated to new test framework as part of
https://github.com/valkey-io/valkey/pull/344, but the old framework
declaration is missed to remove from intset.h. So removed the code.

Signed-off-by: Shivshankar-Reddy <shiva.sheri.github@gmail.com>

src/intset.h

@@ -50,8 +50,4 @@ uint32_t intsetLen(const intset *is);
 size_t intsetBlobLen(intset *is);
 int intsetValidateIntegrity(const unsigned char *is, size_t size, int deep);
 
-#ifdef SERVER_TEST
-int intsetTest(int argc, char *argv[], int flags);
-#endif
-
 #endif // __INTSET_H