Fix '--target_board=native-extended-gdbserver/-m32'

Fix '--target_board=native-extended-gdbserver/-m32'

Running the testsuite with the native-extended-gdbserver.exp board and
passing a variant spec, like

  make check RUNTESTFLAGS="--target_board=native-extended-gdbserver/-m32"

results in dejagnu trying to open a rsh connection to
"native-extended-gdbserver", which of course is wrong.  The point of
this board is running things locally.

The issue is that the native-extended-gdbserver board does not clear
the "isremote" flag properly.

Reported by Sergio at:
  https://sourceware.org/ml/gdb-patches/2015-02/msg00067.html

testsuite/
2015-02-04  Pedro Alves  <palves@redhat.com>

	* boards/native-extended-gdbserver.exp: Remove any target variant
	specifications from the board name before clearing the isremote
	flag from board_info.