Fewer explicit tidyverse dependencies

[mhpob]

This PR removes tibble, magrittr, and tidyr from Imports, further reducing explicit dependencies as requested in #122. Note that glatos still depends on these packages due to dependency on dplyr ("reverse dependency").

glatos depends on dplyr for much of its coding. The functions from tibble and magrittr used by glatos are imported by dplyr; the functions can thus be called via dplyr:: and removed from glatos's Imports.

tidyr is used in one place by one function (read_otn_deployments) to pull yyyy-mm-dd dates from messy inputs. This was replaced using base:sub and a regex capture group. The example of read_otn_deployments results in identical objects.

Current R CMD check failure is due to a floating point issue on macOS which will be fixed with acceptance of #228