yast2-core-devel: removed obsolete dependencies

(flex, sysfsutils and hwinfo-devel)

- 3.1.13
But IMHO flex is still required for the devel package:
[libycp/src/include/ycp/Scanner.h:31:#include "FlexLexer.h"](https://github.com/yast/yast-core/blob/dep_cleanup/libycp/src/include/ycp/Scanner.h#L31)