Hide the dropdown if there are no serial ports detected

**Describe the problem you have/What new integration you would like**
For those running it in docker on a non RPi, this selection is never used as it's always OTA...but it takes up screen real estate, especially on mobile

**Please describe your use case for this integration and alternatives you've tried:**
I've never used this selection as OTA is the only option

**Additional context**
Opening this FR per @glmnet https://github.com/esphome/esphome/commit/a1e10f384e41ebc415b99b533306d55e65c34994#commitcomment-41456889

Start by locating the serial-port selection dropdown and the code that detects available ports, then review the referenced commit for context. Check the Docker-on-non-Raspberry-Pi OTA use case described here. Done means the dropdown is absent when no serial ports are detected while remaining available when ports exist.

Written by the indexing model from the issue text.