Add php7.3 disable commands

[nafiesl]

Hi @samael, I saw your PR (rapidwebltd#4) on rapidwebltd/php-switch-scripts repo. Please allow me to add more improvement to:

1. Add php 7.3 mod disable on ./switch-to-php-5.6.s
2. Add php 7.3 mod disable on ./switch-to-php-7.0.s
3. Add php 7.3 mod disable on ./switch-to-php-7.1.s
4. Add php 7.3 mod disable on ./switch-to-php-7.2.s

Thank you.

[samael]

My carelessness, sorry.

[nafiesl]

Nice, thanks.