Stop using global mesh for custom_partitioning.

[nouiz]

Description

Please include a brief summary of the changes, relevant motivation and context.

Fixes # (issue)

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• 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 not work as expected)
• Infra/Build change
• Code refractor

Changes

Please list the changes introduced in this PR:

• Stop using the global mesh for custom_partitioning. JAX nightly don't need a mesh context anymore. So try to enable that with TE too.

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[ksivaman]

Note: #549

[phu0ngng]

/te-ci jax

[mingxu1067]

LGTM, on the code changes.

[nouiz]

/te-ci jax

[nouiz]

Force pushed the fix as I forgot to sign the commits.