cmd/state_rm: log removed item count

[darkowlzz]

This change adds a line with item count:

$ terraform state rm aws_launch_configuration.mylc1 aws_launch_configuration.mylc2
2 items removed.
Item removal successful.

I feel we can also log "Writing the new state...", which happens right after removal.

Fixes #16109

[apparentlymart]

Thanks for this, @darkowlzz! Looks good to me.

[ghost]

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