Removes unnecessary data.table call from as.data.table.array

[MichaelChirico]

Re-push of the changes in #7010 (authored by @eliocamp) onto Rdatatable/data.table so that we get {atime} results directly here instead of waiting for follow-up.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.69%. Comparing base (73d79ed) to head (4a18f7f).
Report is 97 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7019   +/-   ##
=======================================
  Coverage   98.69%   98.69%           
=======================================
  Files          79       79           
  Lines       14677    14678    +1     
=======================================
+ Hits        14486    14487    +1     
  Misses        191      191           

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[tdhock]

thanks! I added na.rm=FALSE to the atime test to avoid the error.
On my machine I see this result, which indicates a reduction in memory usage, but not much difference in time.

[github-actions]

Generated via commit 4a18f7f

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

Task	Duration
R setup and installing dependencies	4 minutes and 21 seconds
Installing different package versions	8 minutes and 43 seconds
Running and plotting the test cases	2 minutes and 5 seconds

[tdhock]

on CI we do see a small improvement in speed