Remove unused C tracing code in bdb

The `c_call`, `c_return`, and `c_exception` events have historically (since c69ebe8) been dispatched to `c_profilefunc` and never `c_tracefunc`. This commit removes the dead code related to `c_tracefunc` dispatching.

Author: FredericDT

Doc/library/bdb.rst

@@ -192,12 +192,8 @@ The :mod:`bdb` module also defines two classes:
         entered.
       * ``"return"``: A function or other code block is about to return.
       * ``"exception"``: An exception has occurred.
-      * ``"c_call"``: A C function is about to be called.
-      * ``"c_return"``: A C function has returned.
-      * ``"c_exception"``: A C function has raised an exception.
 
-      For the Python events, specialized functions (see below) are called.  For
-      the C events, no action is taken.
+      For the Python events, specialized functions (see below) are called.
 
       The *arg* parameter depends on the previous event.
 

Lib/bdb.py

@@ -267,12 +267,9 @@ def trace_dispatch(self, frame, event, arg):
                   is entered.
             return: A function or other code block is about to return.
             exception: An exception has occurred.
-            c_call: A C function is about to be called.
-            c_return: A C function has returned.
-            c_exception: A C function has raised an exception.
 
         For the Python events, specialized functions (see the dispatch_*()
-        methods) are called.  For the C events, no action is taken.
+        methods) are called.
 
         The arg parameter depends on the previous event.
         """
@@ -288,12 +285,6 @@ def trace_dispatch(self, frame, event, arg):
                 return self.dispatch_return(frame, arg)
             if event == 'exception':
                 return self.dispatch_exception(frame, arg)
-            if event == 'c_call':
-                return self.trace_dispatch
-            if event == 'c_exception':
-                return self.trace_dispatch
-            if event == 'c_return':
-                return self.trace_dispatch
             if event == 'opcode':
                 return self.dispatch_opcode(frame, arg)
             print('bdb.Bdb.dispatch: unknown debugging event:', repr(event))