finish build_target_lib.get_default_sysroot_path migration

This allows us to drop the build_target_lib import from cros_build_lib.

BUG=chromium:1170007
TEST=CQ passes

Change-Id: Icf01d140baa482014acfca800a57db7bb1bdc934
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2810800
Reviewed-by: Sergey Frolov <sfrolov@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/fwgdb.py b/scripts/fwgdb.py
index 6766026..f001ee6 100644
--- a/scripts/fwgdb.py
+++ b/scripts/fwgdb.py
@@ -16,6 +16,7 @@
 
 from elftools.elf.elffile import ELFFile
 
+from chromite.lib import build_target_lib
 from chromite.lib import constants
 from chromite.lib import cros_build_lib
 from chromite.lib import cros_logging as logging
@@ -96,7 +97,8 @@
           (', '.join(unified_build_dirs)))
 
   if not firmware_dir:
-    firmware_dir = os.path.join(cros_build_lib.GetSysroot(board), 'firmware')
+    firmware_dir = os.path.join(
+        build_target_lib.get_default_sysroot_path(board), 'firmware')
 
   # Very old firmware you might still find on GoldenEye had dev.ro.elf.
   basenames = ['dev.elf', 'dev.ro.elf']