Remove suggested `rgdal` as soon as possible

[rsbivand]

raster stopped using rgdal and rgeos in favour of terra in September 2022; rgdal, rgeos and maptools will be archived in October 2023 (see: https://r-spatial.org/r/2023/05/15/evolution4.html, https://r-spatial.github.io/evolution/). When rgdal is not on the library path, this is the CMD check log:
00check.log with test details:
testthat.Rout.zip
Almost certainly, both the Suggests: listing and the test are left over from before #10.

[rsbivand]

@joeroe Please take urgent steps to resolve this issue. No positive changes appear in the repository. Less than three months remain to retain this package on CRAN.

[joeroe]

Thank you for the reminder @rsbivand. This will be on its way to CRAN as soon as they're accepting submissions again (#19).

[rsbivand]

Looks OK when checking without retiring packages on the library path:
00check.log