Remove more explicit return()s thanks to lintr update

[MichaelChirico]

{lintr} removed a lot of false negatives in return_linter():

r-lib/lintr#2779

Basically any function with any argument with defaults could be affected.

[codecov]

Codecov Report

Attention: Patch coverage is 98.36066% with 1 line in your changes missing coverage. Please review.

Project coverage is 98.64%. Comparing base (f78044e) to head (331f5db).

Files with missing lines	Patch %	Lines
R/setkey.R	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6830      +/-   ##
==========================================
- Coverage   98.64%   98.64%   -0.01%     
==========================================
  Files          79       79              
  Lines       14642    14638       -4     
==========================================
- Hits        14444    14439       -5     
- Misses        198      199       +1     

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[github-actions]

Generated via commit 331f5db

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	4 minutes and 39 seconds
Installing different package versions	8 minutes and 9 seconds
Running and plotting the test cases	2 minutes and 20 seconds

[MichaelChirico]

• Use new globbing support from upstream in lintr config #6835
• Remove more explicit return()s thanks to lintr update #6830 👈 (View in Graphite)
• master

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