Clarify PRESUBMIT message for Lacros deprecation

The Lacros platform is deprecated, and its associated code is being removed. Previously, the PRESUBMIT script was updated to recommend transitioning to the IS_CHROMEOS build flag

However, this change introduced ambiguity, leading to the misinterpretation that IS_CHROMEOS_LACROS should be renamed to IS_CHROMEOS alongside the IS_CHROMEOS_ASH build flag.

This CL refines the PRESUBMIT message to clearly state:
1) Code under IS_CHROMEOS_LACROS must be removed.
2) The IS_CHROMEOS_ASH build flag should be renamed to IS_CHROMEOS.

This update aims to eliminate confusion and provide precise guidance during the
deprecation process.

Bug: 388039763
Change-Id: I0cdd7a788da220ecca17f021a1597d2c41b2c05f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6169131
Reviewed-by: Hidehiko Abe <[email protected]>
Reviewed-by: Rick Byers <[email protected]>
Commit-Queue: Maksim Sisov <[email protected]>
Reviewed-by: Georg Neis <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1405919}

Author: msisov

PRESUBMIT.py

@@ -2122,7 +2122,8 @@ class BanRule:
                  r'IS_CHROMEOS_LACROS'),
         explanation=
         ('Lacros is deprecated. Please do not use IS_CHROMEOS_ASH and '
-         'IS_CHROMEOS_LACROS anymore. Prefer IS_CHROMEOS instead.',
+         'IS_CHROMEOS_LACROS anymore. Instead, remove the code section under '
+         'IS_CHROMEOS_LACROS and use IS_CHROMEOS for ChromeOS-only code.',
         ),
         treat_as_error=False,
     ),