Why is my esp8266 still visible under "available connections" when connecting to WiFi?
It's because you don't actively program the WiFi - you just give instructions to configure it, and those instructions are stored elsewhere in flash, separate to a sketch.  The WiFi code is always included and always running regardless of what you include or don't include in your sketch.

Uploading a sketch doesn't replace those settings, and so they remain.

To change the settings you will need to write a sketch that specifically changes them - maybe set it to STA mode, for example.

If you want to completely blank the ESP8266, including the WiFi settings, there is an option in the Tools  menu in the IDE to Erase Flash.