[Fuchsia] Remove deprecated bootserver flag --efi.

"bootserver" fails to run because we are passing it an arg that is now
deprecated, "--efi". EFI partition management is now managed by default
by "bootserver".

Bug: 954277
Change-Id: Id71932b9969a71ef27d21362c010c299659dd459
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574224Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652290}

build/fuchsia/device_target.py

@@ -227,12 +227,6 @@ class DeviceTarget(target.Target):
         EnsurePathExists(boot_data.GetBootImage(self._output_dir,
                                                 self._GetTargetSdkArch()))]
 
-    if self._GetTargetSdkArch() == 'x64':
-      bootserver_command += [
-          '--efi',
-          EnsurePathExists(boot_data.GetTargetFile(self._GetTargetSdkArch(),
-                                                   'local.esp.blk'))]
-
     if self._node_name:
       bootserver_command += ['-n', self._node_name]