remove find_element_by_XXXX

[KazuCocoa]

Other bindings which already had find_element_by_XXX were removed. (e.g. Java client. Ruby client did not have like this syntax)
Python client still has them in selenium repo, so no reason to drop only in this client.
But potentially we'll need to drop them.

Let me leave an issue as a note.

Before removing them, we must print deprecated log in each method

[KazuCocoa]

https://appium.github.io/python-client-sphinx/webdriver.common.html#webdriver.common.appiumby.AppiumBy
https://appium.github.io/python-client-sphinx/webdriver.common.html#module-webdriver.common.mobileby