Get rid of backend parameter whenever possible (#883)

* Get rid of backend parameter whenever possible.

* Always auto-detect if backend choices are 'cryptography' and 'auto', resp. always check cryptography version.

* Improve error message.

* Update documentation.

plugins/modules/openssl_publickey_info.py

@@ -36,6 +36,9 @@ options:
       - Determines which crypto backend to use.
       - The default choice is V(auto), which tries to use C(cryptography) if available.
       - If set to V(cryptography), will try to use the L(cryptography,https://cryptography.io/) library.
+      - Note that with community.crypto 3.0.0, all values behave the same.
+        This option will be deprecated in a later version.
+        We recommend to not set it explicitly.
     type: str
     default: auto
     choices: [auto, cryptography]
@@ -191,9 +194,7 @@ def main():
                 msg=f"Error while reading public key file from disk: {e}", **result
             )
 
-    backend, module_backend = select_backend(
-        module, module.params["select_crypto_backend"], data
-    )
+    module_backend = select_backend(module, data)
 
     try:
         result.update(module_backend.get_info())