fix: Remove unnecessary check in the tck AgentExecutor implementation (#194)

# Description

**NOTE:** This will fail the TCK tests until
a2aproject/a2a-tck#34 is included in a tag
Depends on a2aproject/a2a-tck#34


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<https://www.conventionalcommits.org/> specification.
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Author: fjuma

tck/src/main/java/io/a2a/tck/server/AgentExecutorProducer.java

@@ -29,10 +29,6 @@ private static class FireAndForgetAgentExecutor implements AgentExecutor {
         public void execute(RequestContext context, EventQueue eventQueue) throws JSONRPCError {
             Task task = context.getTask();
 
-            if (context.getMessage().getTaskId() != null && task == null && context.getMessage().getTaskId().startsWith("non-existent")) {
-                throw new TaskNotFoundError();
-            }
-
             if (task == null) {
                 task = new Task.Builder()
                         .id(context.getTaskId())