[Rd] quiet namespace load is noisy

[Lenth, Russell V]

Dear R-devel,

Consider the following clip (in R version 3.6.0, Windows):

    > requireNamespace("ggplot2", quietly = TRUE)
    Registered S3 methods overwritten by 'ggplot2':
      method         from 
      [.quosures     rlang
      c.quosures     rlang
      print.quosures rlang

It seems to me that if one specifies 'quietly = TRUE', then messages about S3 method overrides should be quieted along with everything else. After all, other package startup messages ARE suppressed, and even error messages are suppressed:

    > requireNamespace("xyz", quietly = TRUE)
    > ## (it is silent even though there is no "xyz" package)

Thanks

Russ Lenth
U of Iowa