Ftrack: Don't set FTRACK_SERVER environment variable

[iLLiCiTiT]

Short Description

Don't set FTRACK_SERVER environment variable on openpype process start and don't be dependent on it in code.

Description

At all places where we're dependent on environment variable FTRACK_SERVER should be passed ftrack url to session arguments received from ftrack module instead of using the env variable (probably except farm).

Additional context

Related to PR which changed how ftrack url is received. It requires access to requests module and connection to server which is called on openpype process start.

[cuID:2v2y59v]