Remove pick()

[maurolepore]

The plan is to generalize it as sync(), which would be similar to map() in that it takes any function, but instead of doing the acttion to all items of the list it would do it to only the key one and then propagate the indices to all other elements.

[coveralls]

Pull Request Test Coverage Report for Build 592

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.8%) to 86.384%

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Files with Coverage Reduction	New Missed Lines	%
R/utils.R	2	89.47%
<!--	Total:	2		-->

Totals
Change from base Build 591:	-0.8%
Covered Lines:	590
Relevant Lines:	683

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💛 - Coveralls