Disable padding support.

- Our method of padding messages is not universally supported by
    consuming implementations:

      https://tests.sequoia-pgp.org/#Packet_excess_consumption

  - Disable it for now.  Once we support generating v6 OpenPGP
    messages, we can enable it again with the new padding packet.

src/cli/encrypt.rs

@@ -172,7 +172,7 @@ pub struct Command {
     #[clap(
         long = "compression",
         value_name = "KIND",
-        default_value_t = CompressionMode::Pad,
+        default_value_t = CompressionMode::None,
         help = "Selects compression scheme to use",
         value_enum,
     )]
@@ -198,6 +198,7 @@ pub enum EncryptionMode {
 #[derive(ValueEnum, Debug, Clone)]
 pub enum CompressionMode {
     None,
+    #[cfg(all(unix, not(unix)))] // Bottom, but: `cfg` predicate key cannot be a literal
     Pad,
     Zip,
     Zlib,

src/commands/encrypt.rs

@@ -16,6 +16,7 @@ use openpgp::serialize::stream::LiteralWriter;
 use openpgp::serialize::stream::Message;
 use openpgp::serialize::stream::Recipient;
 use openpgp::serialize::stream::Signer;
+#[cfg(all(unix, not(unix)))] // Bottom, but: `cfg` predicate key cannot be a literal
 use openpgp::serialize::stream::padding::Padder;
 use openpgp::types::CompressionAlgorithm;
 use openpgp::types::KeyFlags;
@@ -186,6 +187,7 @@ pub fn encrypt<'a, 'b: 'a>(
 
     match compression {
         CompressionMode::None => (),
+        #[cfg(all(unix, not(unix)))] // Bottom, but: `cfg` predicate key cannot be a literal
         CompressionMode::Pad => sink = Padder::new(sink).build()?,
         CompressionMode::Zip => sink =
             Compressor::new(sink).algo(CompressionAlgorithm::Zip).build()?,