Remove is_remote kfail from gdb.python/py-evthreads.exp

This testcase works fine with gdbserver nowadays.  So remove the
kfail.

gdb/testsuite/ChangeLog:
2017-10-13  Pedro Alves  <palves@redhat.com>
	    Simon Marchi  <simon.marchi@polymtl.ca>

	PR python/12966
	* gdb.python/py-evthreads.exp: Remove is_remote target kfail.