Linux 3.7 compat, __clear_close_on_exec() removed

Linux 3.7 compat, __clear_close_on_exec() removed

Commit torvalds/linux@b8318b0 moved the __clear_close_on_exec()
function out of include/linux/fdtable.h and in to fs/file.c
making it unavailable to the SPL.

Now as it turns out we only used this function to tear down
some test infrastructure for the vn_getf()/vn_releasef() SPLAT
regression tests.  Rather than implement even more autoconf
compatibilty code to handle this we just remove the test case.
This also allows us to drop three existing autoconf tests.

This does mean the SPLAT tests will no longer verify these
functions but historically they have never been a problem.
And if we feel we absolutely need this test coverage I'm
sure a more portable version of the test case could be added.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #183