PERF: Remove unnecessary(?) asof join functions

Several functions in the join cython are module are basically
just calling others, and can probably be removed. This wouldn't
be a big deal inside python, but in this case it cuts down
considerably on the number of generated cython code.

The tests pass for me locally when I do this and there seems
to be significant space savings. Will provide more detail after
I see CI passing (want to make sure I'm not missing something
first)

Author: wlach

pandas/_libs/join.pyx

@@ -894,55 +894,3 @@ cdef _choose_smaller_timestamp(
         left_indexer[i] = bli[i]
 
     return left_indexer, right_indexer
-
-
-# ----------------------------------------------------------------------
-# asof_join
-# ----------------------------------------------------------------------
-
-def asof_join_backward(numeric_t[:] left_values,
-                       numeric_t[:] right_values,
-                       bint allow_exact_matches=True,
-                       tolerance=None):
-
-    return asof_join_backward_on_X_by_Y(
-        left_values,
-        right_values,
-        None,
-        None,
-        allow_exact_matches=allow_exact_matches,
-        tolerance=tolerance,
-        use_hashtable=False,
-    )
-
-
-def asof_join_forward(numeric_t[:] left_values,
-                      numeric_t[:] right_values,
-                      bint allow_exact_matches=True,
-                      tolerance=None):
-    return asof_join_forward_on_X_by_Y(
-        left_values,
-        right_values,
-        None,
-        None,
-        allow_exact_matches=allow_exact_matches,
-        tolerance=tolerance,
-        use_hashtable=False,
-    )
-
-
-def asof_join_nearest(numeric_t[:] left_values,
-                      numeric_t[:] right_values,
-                      bint allow_exact_matches=True,
-                      tolerance=None):
-
-    cdef:
-        ndarray[intp_t] bli, bri, fli, fri
-
-    # search both forward and backward
-    bli, bri = asof_join_backward(left_values, right_values,
-                                  allow_exact_matches, tolerance)
-    fli, fri = asof_join_forward(left_values, right_values,
-                                 allow_exact_matches, tolerance)
-
-    return _choose_smaller_timestamp(left_values, right_values, bli, bri, fli, fri)

pandas/core/reshape/merge.py

@@ -1691,11 +1691,6 @@ def get_result(self) -> DataFrame:
         return result
 
 
-def _asof_function(direction: str):
-    name = f"asof_join_{direction}"
-    return getattr(libjoin, name, None)
-
-
 def _asof_by_function(direction: str):
     name = f"asof_join_{direction}_on_X_by_Y"
     return getattr(libjoin, name, None)
@@ -2017,8 +2012,8 @@ def injection(obj):
             )
         else:
             # choose appropriate function by type
-            func = _asof_function(self.direction)
-            return func(left_values, right_values, self.allow_exact_matches, tolerance)
+            func = _asof_by_function(self.direction)
+            return func(left_values, right_values, None, None, self.allow_exact_matches, tolerance)
 
 
 def _get_multiindex_indexer(