Revert "finish build_target_lib.get_default_sysroot_path migration"

This reverts commit d8d25cdd41261fcc7dcfe1baf7a1b8a965faf183.

Reason for revert: suspected to cause crbug.com/1196818

BUG=chromium:1196818
TEST=CQ+1 and see if this resolves build issues

Original change's description:
> 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>

Bug: chromium:1170007
Change-Id: I3bb147420bb75b9076a5725a2005e737412aeed0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2811778
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
diff --git a/scripts/cros_gdb.py b/scripts/cros_gdb.py
index 5000160..413154d 100644
--- a/scripts/cros_gdb.py
+++ b/scripts/cros_gdb.py
@@ -19,7 +19,6 @@
 import tempfile
 
 from chromite.cli.cros import cros_chrome_sdk
-from chromite.lib import build_target_lib
 from chromite.lib import commandline
 from chromite.lib import constants
 from chromite.lib import cros_build_lib
@@ -188,7 +187,7 @@
     self.in_chroot = self.IsInChroot()
     self.prompt = '(%s-gdb) ' % self.board
     if self.in_chroot:
-      self.sysroot = build_target_lib.get_default_sysroot_path(self.board)
+      self.sysroot = cros_build_lib.GetSysroot(board=self.board)
       self.inf_cmd = self.RemoveSysrootPrefix(self.inf_cmd)
       self.cross_gdb = self.GetCrossGdb()
     else:
@@ -636,9 +635,8 @@
     gdb_args = options.gdb_args
 
   if inf_cmd:
-    fname = os.path.join(
-        build_target_lib.get_default_sysroot_path(options.board),
-        inf_cmd.lstrip('/'))
+    fname = os.path.join(cros_build_lib.GetSysroot(options.board),
+                         inf_cmd.lstrip('/'))
     if not os.path.exists(fname):
       cros_build_lib.Die('Cannot find program %s.' % fname)
   else: