simplify GPU detection in docker launch script

[sanowl]

Modernize Docker GPU arguments and remove legacy checks

Description

Updated the docker launch script to remove legacy nvidia-docker2 checks and standardize on modern GPU arguments. This simplifies the codebase by removing conditional logic for outdated Docker versions and ensures consistent GPU handling across environments.

Motivation and Context

The script contained a TODO comment indicating to wait until new-style GPU args were widely adopted (estimated 2021). Since we're in 2024 and Docker's native GPU support (introduced in 19.03) is now standard, we can safely remove the legacy compatibility code, making the script cleaner and more maintainable.

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist

• I've read the CONTRIBUTION guide (required)
• I have updated the changelog accordingly (required)
• My change requires a change to the documentation
• I have updated the tests accordingly (required for a bug fix or a new feature)
• I have updated the documentation accordingly
• I have opened an associated PR on the SB3-Contrib repository (if necessary)
• I have opened an associated PR on the RL-Zoo3 repository (if necessary)
• I have reformatted the code using make format (required)
• I have checked the codestyle using make check-codestyle and make lint (required)
• I have ensured make pytest and make type both pass (required)
• I have checked that the documentation builds using make doc (required)

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