Remove icon configuration from default app template.

[freakboy3742]

Remove icon configuration from the default app template. The icons are still included for runtime purposes; but leaving out the icon configuration makes the pedagogical path of teaching icon configuration clearer.

Briefcase-Repo: https://github.com/freakboy3742/briefcase.git
Briefcase-Ref: app-icons

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[mhsmith]

Doesn't this mean the app will contain icons in its source directory, but those icons won't actually be used by Briefcase? Then the user will replace the files and be confused about why it doesn't take effect.

[freakboy3742]

Doesn't this mean the app will contain icons in its source directory, but those icons won't actually be used by Briefcase? Then the user will replace the files and be confused about why it doesn't take effect.

Agreed there's an issue here; I'll consolidate the discussion on beeware/beeware#327