Drop redundant load_composer_autoloader

The extension.json load_composer_autoloader key only require_once's the
extension's own vendor/autoload.php (a file_exists-guarded include,
independent of AutoloadNamespaces). SemanticScribunto has no composer
autoload block and no third-party runtime composer dependencies — its
require lists only php and composer/installers — so there is no local
vendor autoloader worth loading; SMW\Scribunto classes load via
AutoloadNamespaces. Remove the key, matching SemanticCompoundQueries.

Author: alistair3149

extension.json

@@ -31,6 +31,5 @@
 			"i18n"
 		]
 	},
-	"load_composer_autoloader": true,
 	"manifest_version": 2
 }