Tidy up the env secrets handling

The secrets accessor was only used in the tests so remove it.
Skip the memoization, it makes things slightly harder to follow and
it's not needed.

lib/kamal/configuration/env.rb

@@ -1,8 +1,7 @@
 class Kamal::Configuration::Env
   include Kamal::Configuration::Validation
 
-  attr_reader :context
-  attr_reader :clear, :secret_keys
+  attr_reader :context, :clear, :secret_keys
   delegate :argumentize, to: Kamal::Utils
 
   def initialize(config:, secrets:, context: "env")
@@ -11,19 +10,14 @@ class Kamal::Configuration::Env
     @secret_keys = config.fetch("secret", [])
     @context = context
     validate! config, context: context, with: Kamal::Configuration::Validator::Env
-    @secret_map = build_secret_map(@secret_keys)
   end
 
   def clear_args
     argumentize("--env", clear)
   end
 
-  def secrets
-    @resolved_secrets ||= resolve_secrets
-  end
-
   def secrets_io
-    Kamal::EnvFile.new(secrets).to_io
+    Kamal::EnvFile.new(aliased_secrets).to_io
   end
 
   def merge(other)
@@ -33,15 +27,12 @@ class Kamal::Configuration::Env
   end
 
   private
-    def build_secret_map(secret_keys)
-      Array(secret_keys).to_h do |key|
-        key_name, key_aliased_to = key.split(":", 2)
-        key_aliased_to ||= key_name
-        [ key_name, key_aliased_to ]
-      end
+    def aliased_secrets
+      secret_keys.to_h { |key| extract_alias(key) }.transform_values { |secret_key| @secrets[secret_key] }
     end
 
-    def resolve_secrets
-      @secret_map.transform_values { |secret_key| @secrets[secret_key] }
+    def extract_alias(key)
+      key_name, key_aliased_to = key.split(":", 2)
+      [ key_name, key_aliased_to || key_name ]
     end
 end