Revert "Change default target to "create_sdk"."

This reverts commit 4afb45f5b8db311b199ab3ca5a69af8446f63021.

Reason for revert: Going to instead file a bug to get the `all' target appropriately fixed, if possible.

Original change's description:
> Change default target to "create_sdk".
> 
> Currently the "all" target can lead to build errors and is unsupported,
> so fall back to a supported target instead.
> 
> Change-Id: I925a785e4b81ab92e99c3842cb81c338c5a1d990
> Reviewed-on: https://dart-review.googlesource.com/c/87403
> Auto-Submit: Stevie Strickland <sstrickl@google.com>
> Reviewed-by: Zach Anderson <zra@google.com>
> Commit-Queue: Stevie Strickland <sstrickl@google.com>

TBR=zra@google.com,sstrickl@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I27c567ad61e54bd2916027b6e27406bd67eb8330
Reviewed-on: https://dart-review.googlesource.com/c/89140
Reviewed-by: Stevie Strickland <sstrickl@google.com>
Commit-Queue: Stevie Strickland <sstrickl@google.com>
diff --git a/tools/build.py b/tools/build.py
index 3ad9cba..237c486 100755
--- a/tools/build.py
+++ b/tools/build.py
@@ -301,10 +301,9 @@
   if not ProcessOptions(options, args):
     parser.print_help()
     return 1
-  # Determine which targets to build. The default is the "create_sdk" target,
-  # as the "all" target is unsupported and not built on any of the bots.
+  # Determine which targets to build. By default we build the "all" target.
   if len(args) == 0:
-    targets = ['create_sdk']
+    targets = ['all']
   else:
     targets = args