revert(composer): drop DDTrace\\OpenFeature\\ psr-4 mapping

Extension autoloader already handles DDTrace\\OpenFeature\\* via
_files_tracer.php include list when datadog.trace.sources_path is set,
matching how DDTrace\\OpenTelemetry\\* is wired. Keeping the explicit
psr-4 entry split OpenFeature from the OpenTelemetry/OpenTracer pattern.

Test runners must set `-d datadog.trace.sources_path=/path/to/src`
(set automatically by Makefile's TRACER_SOURCES_INI).

Author: leoromanovsky

composer.json

@@ -46,7 +46,6 @@
     },
     "autoload": {
         "psr-4": {
-            "DDTrace\\OpenFeature\\": "./src/DDTrace/OpenFeature/",
             "DDTrace\\": "./src/api/"
         }
     },