opgpcard: Remove ident line from output.

- The certificate generated by admin generate is written to a file,
    prefixed with a line containing the card identifier. That means the
    file is not immediately usable as a pgp certificate.

  - Remove the identifier line.

tools/src/bin/opgpcard/output/generate.rs

@@ -27,10 +27,8 @@ impl AdminGenerate {
     }
 
     fn text(&self) -> Result<String, OpgpCardError> {
-        Ok(format!(
-            "OpenPGP card {}\n\n{}\n",
-            self.ident, self.public_key,
-        ))
+        // Do not print ident, as the file with the public_key must not contain anything else
+        Ok(self.public_key.to_string())
     }
 
     fn v1(&self) -> Result<AdminGenerateV0, OpgpCardError> {