COMPAT: Add back remove_na for seaborn

Closes gh-16971.

pandas/core/dtypes/missing.py

@@ -4,6 +4,7 @@
 import numpy as np
 from pandas._libs import lib
 from pandas._libs.tslib import NaT, iNaT
+from pandas.util._decorators import deprecate
 from .generic import (ABCMultiIndex, ABCSeries,
                       ABCIndexClass, ABCGeneric)
 from .common import (is_string_dtype, is_datetimelike,
@@ -401,3 +402,7 @@ def remove_na_arraylike(arr):
     Return array-like containing only true/non-NaN values, possibly empty.
     """
     return arr[notnull(lib.values_from_object(arr))]
+
+
+# see gh-16971
+remove_na = deprecate("remove_na", remove_na_arraylike)

pandas/core/series.py

@@ -38,6 +38,9 @@
     maybe_cast_to_datetime, maybe_castable)
 from pandas.core.dtypes.missing import isnull, notnull, remove_na_arraylike
 
+# see gh-16971
+from pandas.core.dtypes.missing import remove_na  # noqa
+
 from pandas.core.common import (is_bool_indexer,
                                 _default_index,
                                 _asarray_tuplesafe,

pandas/tests/dtypes/test_missing.py

@@ -14,7 +14,13 @@
 from pandas.core.dtypes.dtypes import DatetimeTZDtype
 from pandas.core.dtypes.missing import (
     array_equivalent, isnull, notnull,
-    na_value_for_dtype)
+    na_value_for_dtype, remove_na)
+
+
+def test_remove_na_deprecation():
+    # see gh-16971
+    with tm.assert_produces_warning(FutureWarning):
+        remove_na(Series([]))
 
 
 def test_notnull():