android how to remove white square shortcut icon from screen
Since your phone is a Lenovo, as can be seen from your screenshots. The feature is called as Wide Touch which adds a floating button on your screen, allowing quick access to system functions.

You can disable Wide Touch in your device's settings. I cannot talk about the exact location of the setting, but for most Lenovo phones, it is in Settings > Features > Wide Touch. 

The feature can be list item within settings or a separate tab. So, please look carefully through the settings.

Here is the link to Lenovo website explaining the feature for S90 smartphone. Your P70 might have it the same way or with minor changes.
https://support.lenovo.com/in/en/solutions/ht102904