Faster list2(), and deprecate rlang_env_dots_values() and rlang_env_dots_list()

[DavisVaughan]

cross::bench_versions(pkgs = c("rlang", "r-lib/rlang#1837"), {
  library(rlang)
  bench::mark(list2(), iterations = 1000000)
})
#> # A tibble: 2 × 7
#>   pkg              expression      min   median `itr/sec` mem_alloc `gc/sec`
#>   <chr>            <bch:expr> <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 rlang            list2()       369ns    492ns  2022173.        0B    156. 
#> 2 r-lib/rlang#1837 list2()       123ns    246ns  3956898.        0B     95.0

cross::bench_versions(pkgs = c("rlang", "r-lib/rlang#1837"), {
  library(rlang)
  x <- 1
  y <- 2
  z <- 3
  bench::mark(list2(x, y, z), iterations = 1000000)
})
#> # A tibble: 2 × 7
#>   pkg              expression          min   median `itr/sec` mem_alloc `gc/sec`
#>   <chr>            <bch:expr>     <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 rlang            list2(x, y, z)    779ns    902ns  1050766.        0B     143.
#> 2 r-lib/rlang#1837 list2(x, y, z)    492ns    656ns  1519305.        0B     176.

cross::bench_versions(pkgs = c("rlang", "r-lib/rlang#1837"), {
  library(rlang)
  x <- as.list(1:1e6)
  bench::mark(list2(!!!x), iterations = 1000000)
})
#> # A tibble: 2 × 7
#>   pkg              expression       min   median `itr/sec` mem_alloc `gc/sec`
#>   <chr>            <bch:expr>  <bch:tm> <bch:tm>     <dbl> <bch:byt>    <dbl>
#> 1 rlang            list2(!!!x)    656ns    861ns  1069517.        0B     17.1
#> 2 r-lib/rlang#1837 list2(!!!x)    410ns    533ns  1673342.        0B     16.7

[DavisVaughan]

I deprecated both of these because vctrs is the only one using them, and now we don't use either