Change sq cert lint to not read from stdin by default.

- Reading from stdin by default has caused confusion.  If the user
    wants to read from stdin, then they should explicitly opt-in.

NEWS

@@ -29,6 +29,7 @@
      certificate store.
    - The user ID argument to `sq key userid revoke` is no longer a
      positional argument, but must be specified with `--userid`.
+   - Change `sq cert lint` to not read from stdin by default.
 * Changes in 0.36.0
  - Missing
 * Changes in 0.35.0

src/cli/cert/lint.rs

@@ -95,6 +95,7 @@ pub struct Command {
     #[clap(
         help = FileOrStdin::HELP_OPTIONAL,
         value_name = FileOrStdin::VALUE_NAME,
+        required = true,
     )]
     pub inputs: Vec<FileOrStdin>,
 

src/commands/cert/lint.rs

@@ -256,11 +256,6 @@ pub fn lint(sq: Sq, mut args: Command) -> Result<()> {
             armor::Kind::PublicKey
         })?;
 
-    // If no inputs are given, read from stdin.
-    if args.inputs.is_empty() {
-        args.inputs.push(Default::default());
-    }
-
     'next_input: for input in args.inputs {
         let mut input_reader = input.open()?;
         let filename = match input.inner() {