HT warnings / probabilities

[macartan]

This message seems unecessary given behavior was specified (in dd it is output for every iteration:

A2 <- declare_estimator(Y ~ Z, estimand = Q, clusters = clusters,
                               model = horvitz_thompson, label = "ht",
                               simple = FALSE)

`simple` = FALSE, using complete cluster randomization

This message seems harder to avoid:

`condition_prs` not found, estimating probability of treatment to be constant at mean of clusters in `condition2` at prob =0.5

Thoughts:

1. If Z_cond_prob is provided as is common in dd can condition_prs not be taken from that (with proper adjustment for those in control)
2. Otherwise can users give this in the function for simple cases (e.g. Z_cond_prob = .5) which is simpler than defining the full condition_pr_mat, or perhaps a vector if there are blocks