crypto: remove ALPN_ENABLED

This constant was likely introduced for feature detection, but it has
been pointless for a long time.

1. I am not aware of any possible Node.js build configuration (on any
   recent/supported release line) that would have crypto.constants but
   not crypto.constants.ALPN_ENABLED.
2. There is no evidence of this constant being used for feature
   detection in the ecosystem. In fact, both internal and external type
   definitions for crypto.constants simply assume that the constant
   exists.
3. There is no good reason for any modern TLS stack to not support ALPN.
   It looks like ALPN might have been optional in much earlier versions
   of OpenSSL, but all recent versions of OpenSSL unconditionally
   support ALPN as far as I can tell.

Refs: https://github.com/nodejs/node/pull/46956
PR-URL: https://github.com/nodejs/node/pull/47028
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

doc/api/crypto.md

@@ -5980,10 +5980,6 @@ See the [list of SSL OP Flags][] for details.
     <td><code>DH_NOT_SUITABLE_GENERATOR</code></td>
     <td></td>
   </tr>
-  <tr>
-    <td><code>ALPN_ENABLED</code></td>
-    <td></td>
-  </tr>
   <tr>
     <td><code>RSA_PKCS1_PADDING</code></td>
     <td></td>

src/node_constants.cc

@@ -1032,9 +1032,6 @@ void DefineCryptoConstants(Local<Object> target) {
     NODE_DEFINE_CONSTANT(target, DH_NOT_SUITABLE_GENERATOR);
 #endif
 
-#define ALPN_ENABLED 1
-    NODE_DEFINE_CONSTANT(target, ALPN_ENABLED);
-
 #ifdef RSA_PKCS1_PADDING
     NODE_DEFINE_CONSTANT(target, RSA_PKCS1_PADDING);
 #endif

typings/internalBinding/constants.d.ts

@@ -243,7 +243,6 @@ declare function InternalBinding(binding: 'constants'): {
     DH_CHECK_P_NOT_PRIME: 1;
     DH_UNABLE_TO_CHECK_GENERATOR: 4;
     DH_NOT_SUITABLE_GENERATOR: 8;
-    ALPN_ENABLED: 1;
     RSA_PKCS1_PADDING: 1;
     RSA_SSLV23_PADDING: 2;
     RSA_NO_PADDING: 3;