pw_assert: Reorganize backends for new pattern

- Move all of the pw_assert_basic implementation into the
  pw_assert_basic.impl target.
- Enable the require_link_deps check for pw_assert.

Change-Id: Ie1f64cf0b7704a51710221d7ef02415c788a6235
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/44100
Commit-Queue: Wyatt Hepler <hepler@google.com>
Pigweed-Auto-Submit: Wyatt Hepler <hepler@google.com>
Reviewed-by: Ewout van Bekkum <ewout@google.com>
diff --git a/pw_assert_log/BUILD.gn b/pw_assert_log/BUILD.gn
index 46ce4c8..742c8be 100644
--- a/pw_assert_log/BUILD.gn
+++ b/pw_assert_log/BUILD.gn
@@ -46,9 +46,8 @@
   sources = [ "assert_log.cc" ]
 }
 
-# TODO(pwbug/372): Reorganize this.
-# pw_assert_log doesn't have deps with potential circular dependencies, so
-# "deps" can be empty.
+# pw_assert_log doesn't have deps with potential circular dependencies, so this
+# impl group can be empty.
 group("pw_assert_log.impl") {
 }