Remove feature = "frequency-bridging"

[mattheworris]

Description

Bridging is a core feature of Frequency and once deployed will not need to be configured conditionally.
See also #2367 when re-factoring features.

Notes

• node/cli/src/command.rs is confusing. Originally used to build a runtime for use with the Snowbridge Zombienet configuration, this setup may be helpful in determining how to run Frequency with bridging locally.

Related Issues

• Refactor: Remove #cfg statement and resulting redundant code #2513
• Refactor: Create bridging_runtime.rs to encapsulate runtime/frequency/src/lib.rs changes for bridging #2514
• Chore: frequency-bridging should be added to CI #2517

Acceptance Criteria

• frequency-bridging feature flag removed