Remove "this interpretation is optional" from COPYING

[Miepee]

If any application uses part of a GPLv3 licensed software, it has to provide full source code under the same license. The only exceptions are for plugin cases where both programs are treated as two distinct programs.

In order to avoid confusion from people not knowing how the GPLv3 works treating the COPYING file as "the correct tldr interpretation", I omitted the part of the file that mentions that the "viralization" part of the gplv3 is optional.

See:

• https://www.gnu.org/licenses/gpl-faq.html#GPLInProprietarySystem
• https://www.gnu.org/licenses/gpl-faq.html#GPLPlugins

[Alcaro]

"This interpretation" doesn't refer to GPL virality - it refers to that specific COPYING file. If keeping that interpretation is mandatory, then that effectively makes Flips use a custom license. It's staying optional.

But I agree it's badly worded.