Reconsider `use_tidy_eval()`

[hadley]

It's no longer necessary since in most cases you don't need to use any rlang functions.

@lionel-

[ijlyttle]

FWIW, for the "Building Tidy Tools" course, we ended up doing:

usethis::use_import_from("rlang", c(".data", ".env"))
usethis::use_import_from("rlang", ":=") # later on