Remove assistant crate (#30168)

This PR removes the `assistant` crate, as it is no longer used.

Release Notes:

- N/A

assets/keymaps/default-linux.json

@@ -213,21 +213,6 @@
       "ctrl-shift-n": "agent::RejectAll"
     }
   },
-  {
-    "context": "AssistantPanel",
-    "bindings": {
-      "ctrl-k c": "assistant::CopyCode",
-      "ctrl-shift-e": "project_panel::ToggleFocus",
-      "ctrl-g": "search::SelectNextMatch",
-      "ctrl-shift-g": "search::SelectPreviousMatch",
-      "ctrl-alt-/": "agent::ToggleModelSelector",
-      "ctrl-k h": "assistant::DeployHistory",
-      "ctrl-k l": "agent::OpenRulesLibrary",
-      "new": "assistant::NewChat",
-      "ctrl-t": "assistant::NewChat",
-      "ctrl-n": "assistant::NewChat"
-    }
-  },
   {
     "context": "ContextEditor > Editor",
     "bindings": {
@@ -713,8 +698,8 @@
   {
     "context": "PromptEditor",
     "bindings": {
-      "ctrl-[": "assistant::CyclePreviousInlineAssist",
-      "ctrl-]": "assistant::CycleNextInlineAssist",
+      "ctrl-[": "agent::CyclePreviousInlineAssist",
+      "ctrl-]": "agent::CycleNextInlineAssist",
       "ctrl-alt-e": "agent::RemoveAllContext"
     }
   },

assets/keymaps/default-macos.json

@@ -258,21 +258,6 @@
       "shift-ctrl-r": "agent::OpenAgentDiff"
     }
   },
-  {
-    "context": "AssistantPanel",
-    "use_key_equivalents": true,
-    "bindings": {
-      "cmd-k c": "assistant::CopyCode",
-      "cmd-shift-e": "project_panel::ToggleFocus",
-      "cmd-g": "search::SelectNextMatch",
-      "cmd-shift-g": "search::SelectPreviousMatch",
-      "cmd-alt-/": "agent::ToggleModelSelector",
-      "cmd-k h": "assistant::DeployHistory",
-      "cmd-k l": "agent::OpenRulesLibrary",
-      "cmd-t": "assistant::NewChat",
-      "cmd-n": "assistant::NewChat"
-    }
-  },
   {
     "context": "ContextEditor > Editor",
     "use_key_equivalents": true,
@@ -780,8 +765,8 @@
       "cmd-shift-a": "agent::ToggleContextPicker",
       "cmd-alt-/": "agent::ToggleModelSelector",
       "cmd-alt-e": "agent::RemoveAllContext",
-      "ctrl-[": "assistant::CyclePreviousInlineAssist",
-      "ctrl-]": "assistant::CycleNextInlineAssist"
+      "ctrl-[": "agent::CyclePreviousInlineAssist",
+      "ctrl-]": "agent::CycleNextInlineAssist"
     }
   },
   {