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

Cargo.lock

@@ -62,7 +62,6 @@ dependencies = [
  "chrono",
  "client",
  "collections",
- "command_palette_hooks",
  "component",
  "context_server",
  "convert_case 0.8.0",
@@ -547,7 +546,6 @@ dependencies = [
  "collections",
  "context_server",
  "editor",
- "feature_flags",
  "fs",
  "futures 0.3.31",
  "fuzzy",
@@ -597,7 +595,6 @@ dependencies = [
  "anyhow",
  "collections",
  "deepseek",
- "feature_flags",
  "fs",
  "gpui",
  "indexmap",
@@ -15088,7 +15085,6 @@ dependencies = [
  "client",
  "collections",
  "db",
- "feature_flags",
  "gpui",
  "http_client",
  "notifications",