scripts: runner: nrfjprog: remove BOARD environment requirement

The BOARD variable has been removed from the environment provided to
runners. It's not being used to flash the board, so just remove the
check for it to avoid an exception at runtime.

Signed-off-by: Marti Bolivar <marti@opensourcefoundries.com>
diff --git a/scripts/support/runner/nrfjprog.py b/scripts/support/runner/nrfjprog.py
index d326a73..f11ab8f 100644
--- a/scripts/support/runner/nrfjprog.py
+++ b/scripts/support/runner/nrfjprog.py
@@ -13,11 +13,10 @@
 class NrfJprogBinaryRunner(ZephyrBinaryRunner):
     '''Runner front-end for nrfjprog.'''
 
-    def __init__(self, hex_, family, board, debug=False):
+    def __init__(self, hex_, family, debug=False):
         super(NrfJprogBinaryRunner, self).__init__(debug=debug)
         self.hex_ = hex_
         self.family = family
-        self.board = board
 
     def replaces_shell_script(shell_script, command):
         return command == 'flash' and shell_script == 'nrf_flash.sh'
@@ -30,14 +29,12 @@
         - O: build output directory
         - KERNEL_HEX_NAME: name of kernel binary in ELF format
         - NRF_FAMILY: e.g. NRF51 or NRF52
-        - BOARD: Zephyr board name
         '''
         hex_ = path.join(get_env_or_bail('O'),
                          get_env_or_bail('KERNEL_HEX_NAME'))
         family = get_env_or_bail('NRF_FAMILY')
-        board = get_env_or_bail('BOARD')
 
-        return NrfJprogBinaryRunner(hex_, family, board, debug=debug)
+        return NrfJprogBinaryRunner(hex_, family, debug=debug)
 
     def get_board_snr_from_user(self):
         snrs = self.check_output(['nrfjprog', '--ids'])
@@ -92,5 +89,5 @@
         for cmd in commands:
             self.check_call(cmd)
 
-        print('{} Serial Number {} flashed with success.'.format(
-                  self.board, board_snr))
+        print('Board with serial number {} flashed successfully.'.format(
+                  board_snr))