remove unused import #131

Job	Run time
R Package Checks / revdeps-check	0s
R Package Checks / codecov / test-coverage (ubuntu-latest)	1m 49s
R Package Checks / check-R-updates / updated-files	3s
R Package Checks / codecov / test-coverage (windows-latest)	1m 38s
R Package Checks / codecov / test-coverage (macOS-latest)	1m 31s
R Package Checks / deps-main-check / deps-main	1m 26s
R Package Checks / lintr / lint	1m 35s
R Package Checks / docs-check / docs-check	3m 4s
R Package Checks / r-cmd-check / macOS-latest (release)	1m 29s
R Package Checks / r-cmd-check / windows-latest (release)	2m 36s
R Package Checks / r-cmd-check / windows-latest (4.1)	5m 0s
R Package Checks / r-cmd-check / ubuntu-latest (release)	1m 43s
R Package Checks / r-cmd-check / ubuntu-latest (devel)	1m 43s
R Package Checks / r-cmd-check / ubuntu-latest (oldrel-1)	1m 57s
R Package Checks / r-cmd-check / ubuntu-latest (oldrel-2)	2m 8s
R Package Checks / r-cmd-check / ubuntu-latest (oldrel-3)	1m 57s
R Package Checks / version-check / version-check	48s
	30m 27s

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