chore: remove useless persistent install instructions

Description

eDrive is not a persistent app anymore and can be installed as a regular one. So we can remove the persistent specific install instructions.

Screenshots

Technical details

Tests

Issues

10 commandments of code reviews

👪 ❤ https://gitlab.e.foundation/internal/wiki/-/wikis/mobile-team/guidelines/Code-review

Summary by CodeRabbit

• Documentation
  • Updated README to focus on the purpose of eDrive application in synchronizing user data files to /e/Cloud or a self-hosted cloud.
  • Removed installation instructions for eDrive application.