Remove unnecessary code from books reducer

[UncleJimmy]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: 1264

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[coveralls]

Coverage remained the same at 88.615% when pulling 47eeb32 on UncleJimmy:hotfix-1264 into 4223ff9 on ngrx:master.

[brandonroberts]

Thanks @UncleJimmy!