Fix dual notification when deleting bitstreamformats

[artlowel]

References

• Fixes Deleting a Bitstream Format shows an error even though it works #1882

Description

The issue here was older, likely introduced by #975: the BitstreamFormatDataService had been refactored to work using RemoteData objects, but the delete method in the component wasn't updated afterwards. As a consequence the error notification is shown when the dataService emits the first time, to indicate that the response is pending. When it emits again afterwards, once the response comes in, the success notification is shown.

The solution was to add a getFirstCompletedRemoteData() operator

I also refactored the delete method to get rid of the nested subscribes

Instructions for Reviewers

Delete bitstreamformats separately and in bulk, and verify that they are removed correctly, and that only the correct notifications are shown.

Checklist

• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes TSLint validation using yarn run lint
• My PR doesn't introduce circular dependencies
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• If my PR includes new, third-party dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.

[lgtm-com]

This pull request introduces 2 alerts when merging f5deb88 into 8ffc325 - view on LGTM.com

new alerts:

• 2 for Unused variable, import, function or class

[tdonohue]

👍 Thanks @artlowel . Tested this today and it fixes the bug.