agent: Remove feature flag checks (#30055)

This PR removes all of the feature flag checks related to the Agent.

Tried to do this in the least invasive way possible; we can follow up
with a full removal.

Release Notes:

- N/A

crates/agent/Cargo.toml

@@ -29,7 +29,6 @@ buffer_diff.workspace = true
 chrono.workspace = true
 client.workspace = true
 collections.workspace = true
-command_palette_hooks.workspace = true
 component.workspace = true
 context_server.workspace = true
 convert_case.workspace = true