fix(api): deprecate nvim_subscribe, nvim_unsubscribe #30456

Problem:
- nvim_subscribe, nvim_unsubscribe were deprecated in
  aec4938a21a02d279d13a9eb64ef3b7cc592c374 but this wasn't set in the
  API metadata.
- The function annotations
  ```
  FUNC_API_SINCE(1) FUNC_API_REMOTE_ONLY FUNC_API_DEPRECATED_SINCE(13)
  ```
  cause this test to fail:
   ```
   RUN T3 api metadata functions are compatible with old metadata or have new level: 3.00 ms ERR
   test/functional/api/version_spec.lua:135: function vim_subscribe was removed but exists in level 0 which nvim should be compatible with
   stack traceback:
     test/functional/api/version_spec.lua:135: in function <test/functional/api/version_spec.lua:128>
   ```

Solution:
- Set the API metadata.
- Rearrange the annotations so that FUNC_API_DEPRECATED_SINCE is 2nd:
  ```
  FUNC_API_SINCE(1) FUNC_API_DEPRECATED_SINCE(13) FUNC_API_REMOTE_ONLY
  ```

1 files changed, 4 insertions, 2 deletions

diff --git a/src/nvim/api/deprecated.c b/src/nvim/api/deprecated.c
index 493856905f..51ed6eaa41 100644
--- a/src/nvim/api/deprecated.c
+++ b/src/nvim/api/deprecated.c
@@ -798,7 +798,8 @@ theend:
 /// @param channel_id Channel id (passed automatically by the dispatcher)
 /// @param event      Event type string
 void nvim_subscribe(uint64_t channel_id, String event)
-  FUNC_API_SINCE(1) FUNC_API_REMOTE_ONLY
+// XXX: c_grammar.lua is order-sensitive.
+  FUNC_API_SINCE(1) FUNC_API_DEPRECATED_SINCE(13) FUNC_API_REMOTE_ONLY
 {
   // Does nothing. `rpcnotify(0,…)` broadcasts to all channels, there are no "subscriptions".
 }
@@ -808,7 +809,8 @@ void nvim_subscribe(uint64_t channel_id, String event)
 /// @param channel_id Channel id (passed automatically by the dispatcher)
 /// @param event      Event type string
 void nvim_unsubscribe(uint64_t channel_id, String event)
-  FUNC_API_SINCE(1) FUNC_API_REMOTE_ONLY
+// XXX: c_grammar.lua is order-sensitive.
+  FUNC_API_SINCE(1) FUNC_API_DEPRECATED_SINCE(13) FUNC_API_REMOTE_ONLY
 {
   // Does nothing. `rpcnotify(0,…)` broadcasts to all channels, there are no "subscriptions".
 }