exec: Remove outdated doc

src/command/exec.rs

@@ -14,10 +14,6 @@ use crate::util::{self, CommandExecution};
 pub fn subcommand() -> App<'static, 'static> {
     let command = SubCommand::with_name("exec")
         .about("Run a command on remote machines")
-        .long_about(r#"Run a command on remote machines
-
-By default, Colmena will print out all output lines. Use --oneline for a condensed status output with each node taking up a single line.
-"#)
         .setting(AppSettings::TrailingVarArg)
         .arg(Arg::with_name("parallel")
             .short("p")