javadoc, do not generate default javadoc description if description is not defined in tsp/swagger

[haolingdong-msft]

Link #2776

We generate a dummy description e.g. "The configuration property." in below example if both description and summary are not defined on the model property or client method parameter. It is meaningless and we cannot easily distinguish whether the javadoc is dummy or created by service team. So we would like to remove it.

 /**
+     * Set the configuration property: The configuration property.
     * 
     * @param configuration the configuration value to set.
     * @return the JobData object itself.
     */
    @Generated
    public JobData setConfiguration(String configuration) {
        this.configuration = configuration;
        return this;
    }

[weidongxu-microsoft]

This applies to @param (and in some cases, the @return) as well.