JIRA: https://jira.spring.io/browse/INT-4147
By default `FileReadingMessageSource` is created without `filter`, at the same time internal `WatchServiceDirectoryScanner` is supplied with default `filter` by its `DefaultDirectoryScanner` super class.
A `DELETE` watch event condition around `FileReadingMessageSource.this.filter` is wrong, because it is `null` by default. Therefore `DELETE` events never succeed
* Modify `FileInboundTransactionTests` to accept `DELETE` watch event as well and verify that `ResettableFileListFilter.remove(File)` is performed
* Call newly created getter for `DefaultDirectoryScanner.filter` in the `WatchServiceDirectoryScanner` to assert against supplied `filter`
Polishing
**Cherry-pick to 4.3.x**
Conflicts:
spring-integration-file/src/main/java/org/springframework/integration/file/DefaultDirectoryScanner.java
Resolved.
4653090686