Update loader.neon and remove obsolete nullCoalesce.variable.neon

Author: warcooft

utils/phpstan-baseline/loader.neon

@@ -23,7 +23,6 @@ includes:
     - missingType.return.neon
     - notIdentical.alwaysTrue.neon
     - nullCoalesce.property.neon
-    - nullCoalesce.variable.neon
     - offsetAccess.notFound.neon
     - property.defaultValue.neon
     - property.nonObject.neon