Remove topic must differ from mqttclient

[barbudor]

Description:

Removing an old constraint that Topic/ButtonTopic/SwitchTopic/GroupTopic should be different from MqttClient as the reasons for that are no more present.
Still enforce that GroupTopic should be different from Topic to avoid double subscription.

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works with Tasmota core ESP32 V.2.0.1.1
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass

[arendst]

Thx.