Revert "Add user_rf_pre_init() function to fix build error with SDK-1.1.0"
Revert "Add user_rf_pre_init() function to fix build error with SDK-1.1.0"

This reverts commit 5ff97669081782aa3acfba012372ec487c3fbe03.

The esp-onen-sdk adds the fix for force-requiring user_rf_pre_init() [1].
So we need to drop the user_rf_pre_init function in user_main.c to prevent
multiple definition of `user_rf_pre_init' error.

[1] https://github.com/pfalcon/esp-open-sdk/commit/4e4590de89bc1524f6b7e7c35744325f9dc2e27b

sreeisalso/esp_mqtt,tuanpmt/esp_mqtt,tuanpmt/esp_mqtt,sreeisalso/esp_mqtt