[VM/Debugger] Delete a TODO

I didn't mean to commit this TODO, it was just a reminder I left as I was working on a CL.

TEST=CI

Change-Id: I5e3f7592bd4d7d92f85b92ef44c6adf26465c772
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/388380
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Derek Xu <derekx@google.com>

runtime/vm/debugger.h

@@ -884,8 +884,6 @@ class Debugger {
   // If any other |ErrorPtr| is returned, it means that a |BreakpointLocation|
   // was not prepared successfully, and the return value will point to an
   // |Error| describing why the |BreakpointLocation| could not be prepared.
-  // TODO(derekxu16): Continue looking at all usages of functions that return
-  // |ErrorPtr|s and account for Object::no_debuggable_code_error().
   ErrorPtr SetBreakpoint(const GrowableHandlePtrArray<const Script>& scripts,
                          TokenPosition token_pos,
                          TokenPosition last_token_pos,