[nnbd_migration] Fix #41795, delete/change hint causes rerun.

This is only an issue for the old style (not in stacktrace) buttons.

I did not add a test for this; there are many tests for this code in the
new workflow, inside UnitInfo.handleSourceEdit, etc, and this code path
will be removed soon hopefully.

I *did* test manually and saw that it works.

Change-Id: Iac8ba4cb775b9b15c8db1c1cadd4701da81452be
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149382
Commit-Queue: Paul Berry <paulberry@google.com>
Auto-Submit: Mike Fairhurst <mfairhurst@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>

https://dart.googlesource.com/sdk/+/42b71b8f9e1dd8730e89321e760cd0579afc5125
diff --git a/commits.json b/commits.json
index ff73135..4e0278f 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"c5d012900f7db0dc5dc9afb46f76d16b87915db0",
   "external/github.com/flutter/flutter":"a1636b6fef2ebe7840ba6dc1b3f9d77095ef3b45",
-  "sdk":"83277a4f3793271c372b649b87a80eba1d1c383b"
+  "sdk":"42b71b8f9e1dd8730e89321e760cd0579afc5125"
 }
\ No newline at end of file