Remove usage of shebang in examples

[approxit]

While working on #1086, my changes on windows machine implicitly changed file permissions for one of example python scripts. Goth tests are running on linux and are executing example code via:

$ ./example.py

which checks executable permission on file. Implicit switch from 755 to 644 dropped that permission, and test was failing.

We should not be prone to this kind of quirks, and there is no actual need to keep using shebangs. In fact using it expects python to be available in particular way, which may differ vastly from user to user.

Todo

• Remove shebangs from all examples
• Change example invocation on goth tests