Don't default the taskExecutor to avoid overload confusion

Author: ktoso

stdlib/public/Concurrency/Task+init.swift.gyb

@@ -54,7 +54,7 @@ import Swift
 %   ],
 %   [ # PARAMS
 %     'name: String? = nil',
-%     'executorPreference taskExecutor: (any TaskExecutor)? = nil',
+%     'executorPreference taskExecutor: (any TaskExecutor)?',
 %     'priority: TaskPriority? = nil',
 %     # '@_inheritActorContext @_implicitSelfCapture operation: sending @escaping @isolated(any) () async throws -> Success',
 %     'operation: sending @escaping () async throws -> Success',
@@ -70,7 +70,7 @@ import Swift
 %   ],
 %   [ # PARAMS
 %     'name: String? = nil',
-%     'executorPreference taskExecutor: (any TaskExecutor)? = nil',
+%     'executorPreference taskExecutor: (any TaskExecutor)?',
 %     'priority: TaskPriority? = nil',
 %     'operation: sending @escaping () async throws -> Success',
 %   ]),