Problem: feed_command, nvim_buf_set_option, nvim_buf_get_number, and exc_exec
are marked as deprecated.
Solution: Remove them from the test units in api/buffer_spec, autocmd/focus_spec,
ui/input_spec, and editor/put_spec.
Some test units only used a few deprecated functions, so creating a separate PR
for each would be excessive. Therefore, several were combined into a single PR.