finish build_target_lib.get_default_sysroot_path migration [reland]

This allows us to drop the build_target_lib import from cros_build_lib.

The failing platform2 code that caused this to revert before has been
fixed, and cs/ doesn't show any other latent hits.

BUG=chromium:1170007
TEST=CQ passes

Change-Id: I284d99fc2570eff7c4e843140efdfe5a56acc8d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2814898
Tested-by: Mike Frysinger <vapier@chromium.org>
Auto-Submit: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Sergey Frolov <sfrolov@google.com>
Reviewed-by: Sergey Frolov <sfrolov@google.com>
diff --git a/scripts/parallel_emerge.py b/scripts/parallel_emerge.py
index 5441e29..7d29a6f 100644
--- a/scripts/parallel_emerge.py
+++ b/scripts/parallel_emerge.py
@@ -20,9 +20,9 @@
 import os
 import sys
 
+from chromite.lib import build_target_lib
 from chromite.lib import commandline
 from chromite.lib import constants
-from chromite.lib import cros_build_lib
 
 
 assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
@@ -32,7 +32,7 @@
   """Translates board argument to sysroot location."""
 
   def __call__(self, parser, namespace, values, option_string=None):
-    sysroot = cros_build_lib.GetSysroot(values)
+    sysroot = build_target_lib.get_default_sysroot_path(values)
     setattr(namespace, 'sysroot', sysroot)