sbrk/sbrk01.c: cleanup

* Delete some useless commtents.
* Move the test body from main() to sbrk_verify().
* Remove tst_tmpdir().
* Some cleanup.
* Skip sbrk directory on uClinux
  (instead of the UCLINUX ifdefs in the C source)

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Signed-off-by: Cyril Hrubis <chrubis@suse.cz>