Remove redundant isCanceled checks in SaveablesList and SaveableHelper

[vogella]

This addresses the proposal by ptziegler in PR #3542 to split the removal of isCanceled checks.

[github-actions]

Test Results

 3 018 files  ±0   3 018 suites  ±0   2h 21m 57s ⏱️ -58s
 8 242 tests ±0   7 993 ✅  - 1  248 💤 ±0  1 ❌ +1 
23 646 runs  ±0  22 854 ✅  - 1  791 💤 ±0  1 ❌ +1 

For more details on these failures, see this check.

Results for commit 7d16b28. ± Comparison against base commit e15e9bf.

[ptziegler]

The call of newChild() has been changed to split() as part of 'Bug 479879 - Adopt SubMonitor.split in platform UI'. For those classes specifically in c7cb5c4.

These methods throw an OperationCanceledException if the monitor has been canceled by the user. If there are any side-effects from throwing an exception, they would've become apparent by now.

I would even go so far and say that simply breaking out of the loop is an anti-pattern, because the program could now continue in a partially saved state, rather than properly handling the cancellation.

[ptziegler]

The test case has been sporadically failing and is tracked via #3581. It should be irrelevant to this change.

[vogella]

Thanks @ptziegler