Temporarily revert "Test changing base method to async after (#1464)" (#1493)

Temporarily revert commit 31ec38a (PR #1464) so that it will not be
included in the upcoming 7.2.0 release as discussed in
#1464 (comment).
This will be re-applied to the `main` branch after the 7.2.0 release.

Author: JohanMabille

ipykernel/kernelbase.py

@@ -869,7 +869,7 @@ async def execute_request(self, stream, ident, parent):
             subshell_id = parent["header"].get("subshell_id")
             self._abort_queues(subshell_id)
 
-    async def do_execute(
+    def do_execute(
         self,
         code,
         silent,
@@ -904,7 +904,7 @@ async def complete_request(self, stream, ident, parent):
         matches = json_clean(matches)
         self.session.send(stream, "complete_reply", matches, parent, ident)
 
-    async def do_complete(self, code, cursor_pos):
+    def do_complete(self, code, cursor_pos):
         """Override in subclasses to find completions."""
         return {
             "matches": [],
@@ -940,7 +940,7 @@ async def inspect_request(self, stream, ident, parent):
         msg = self.session.send(stream, "inspect_reply", reply_content, parent, ident)
         self.log.debug("%s", msg)
 
-    async def do_inspect(self, code, cursor_pos, detail_level=0, omit_sections=()):
+    def do_inspect(self, code, cursor_pos, detail_level=0, omit_sections=()):
         """Override in subclasses to allow introspection."""
         return {"status": "ok", "data": {}, "metadata": {}, "found": False}
 
@@ -964,7 +964,7 @@ async def history_request(self, stream, ident, parent):
         msg = self.session.send(stream, "history_reply", reply_content, parent, ident)
         self.log.debug("%s", msg)
 
-    async def do_history(
+    def do_history(
         self,
         hist_access_type,
         output,
@@ -1104,7 +1104,7 @@ async def shutdown_request(self, stream, ident, parent):
             shell_io_loop = self.shell_stream.io_loop
             shell_io_loop.add_callback(shell_io_loop.stop)
 
-    async def do_shutdown(self, restart):
+    def do_shutdown(self, restart):
         """Override in subclasses to do things when the frontend shuts down the
         kernel.
         """
@@ -1130,7 +1130,7 @@ async def is_complete_request(self, stream, ident, parent):
         reply_msg = self.session.send(stream, "is_complete_reply", reply_content, parent, ident)
         self.log.debug("%s", reply_msg)
 
-    async def do_is_complete(self, code):
+    def do_is_complete(self, code):
         """Override in subclasses to find completions."""
         return {"status": "unknown"}