[Fuchsia] Remove checkout_aemu from DEPS.

Remove checkout_aemu variable from DEPS.
Make tests run by default in AEMU instead of QEMU for x64 Fuchsia.

Bug: 1000907
Change-Id: I5cbe6fa2129b4f8a335fe629e942eecbe88d23fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2037021Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Kevin Marshall <kmarshall@chromium.org>
Commit-Queue: Chong Gu <chonggu@google.com>
Cr-Commit-Position: refs/heads/master@{#738817}

DEPS

@@ -134,11 +134,6 @@ vars = {
   # qemu on linux-arm64 machines.
   'checkout_fuchsia_for_arm64_host': False,
 
-  # By Default, do not checkout AEMU, as it is too big. This can be overridden
-  # e.g. with custom_vars.
-  # TODO(chonggu): Delete once AEMU package is small enough.
-  'checkout_aemu': False,
-
   # Default to the empty board. Desktop Chrome OS builds don't need cros SDK
   # dependencies. Other Chrome OS builds should always define this explicitly.
   'cros_board': '',

build/fuchsia/common_args.py

@@ -130,9 +130,13 @@ def GetDeploymentTargetForArgs(args, require_kvm=False):
   else:
     system_log_file = None
 
-  # Allow fuchsia to run on qemu if device not explicitly chosen.
+  # Allow fuchsia to run on emulator if device not explicitly chosen.
+  # AEMU is the default emulator for x64 Fuchsia, and QEMU for others.
   if not args.device:
-    args.device = 'qemu'
+    if args.target_cpu == 'x64':
+      args.device = 'aemu'
+    else:
+      args.device = 'qemu'
 
   target_args = { 'output_dir':args.output_directory,
                   'target_cpu':args.target_cpu,

testing/buildbot/waterfalls.pyl

@@ -1872,7 +1872,6 @@
           'all',
         ],
         'mixins': [
-          'fuchsia_aemu',
           'linux-xenial',
         ],
         'swarming': {
@@ -1891,7 +1890,6 @@
           'all',
         ],
         'mixins': [
-          'fuchsia_aemu',
           'linux-xenial',
         ],
         'swarming': {