transition to survival's `nobs()` methods

[simonpcouch]

On devtools::document():

Registered S3 methods overwritten by 'survival':
  method       from 
  nobs.coxph   broom
  nobs.survreg broom

[simonpcouch]

The definitions of nobs.survreg() are identical, so we can just remove broom's method. For coxph:

survival:::nobs.coxph
function (object, ...) 
object$nevent
<bytecode: 0x16cc8f0e0>
<environment: namespace:survival>

while in broom:

nobs.coxph
function(object, ...) {
  length(object$linear.predictors)
}
<environment: namespace:broom>

broom's definition is copied over for its nobs.survreg(), it seems.

Wooooof. With the fit objects from the tests:

for (f in list(fit, fit2, fit3, fit4, fit5, fit6)) {
  cat(paste0(survival:::nobs.coxph(f), " ", broom:::nobs.coxph(f)))
  cat("\n")
}
#> 165 228
#> 165 228
#> 164 227
#> 112 340
#> 897 1822
#> 897 1822

[github-actions[bot]]

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