remove a deprecated special function (after #21819)

src/sage/functions/special.py

@@ -142,7 +142,7 @@
    by hardware floats precision.
 """
 
-#*****************************************************************************
+# ****************************************************************************
 #       Copyright (C) 2006 William Stein <wstein@gmail.com>
 #                     2006 David Joyner <wdj@usna.edu>
 #
@@ -155,8 +155,8 @@
 #
 #  The full text of the GPL is available at:
 #
-#                  http://www.gnu.org/licenses/
-#*****************************************************************************
+#                  https://www.gnu.org/licenses/
+# ****************************************************************************
 
 from sage.rings.integer import Integer
 from sage.rings.real_mpfr import RealField
@@ -174,6 +174,7 @@
 from sage.functions.all import sqrt, sin, cot, exp
 from sage.symbolic.all import I
 
+
 class SphericalHarmonic(BuiltinFunction):
     r"""
     Returns the spherical harmonic function `Y_n^m(\theta, \varphi)`.
@@ -1014,23 +1015,3 @@ def _print_latex_(self, n, z, m):
         return r"\Pi(%s,%s,%s)" % (latex(n), latex(z), latex(m))
 
 elliptic_pi = EllipticPi()
-
-
-def error_fcn(x):
-    """
-    Deprecated in :trac:`21819`. Please use ``erfc()``.
-
-    EXAMPLES::
-
-        sage: error_fcn(x)
-        doctest:warning
-        ...
-        DeprecationWarning: error_fcn() is deprecated. Please use erfc()
-        See http://trac.sagemath.org/21819 for details.
-        erfc(x)
-    """
-    from .error import erfc
-    from sage.misc.superseded import deprecation
-    deprecation(21819, "error_fcn() is deprecated. Please use erfc()")
-    return erfc(x)
-