RF: remove from_filespec classmethod

It was already broken, and has been deprecated since version 1.0.

Author: matthew-brett

nibabel/filebasedimages.py

@@ -268,14 +268,6 @@ def from_filename(klass, filename):
         file_map = klass.filespec_to_file_map(filename)
         return klass.from_file_map(file_map)
 
-    @classmethod
-    def from_filespec(klass, filespec):
-        warnings.warn('``from_filespec`` class method is deprecated\n'
-                      'Please use the ``from_filename`` class method '
-                      'instead',
-                      DeprecationWarning, stacklevel=2)
-        klass.from_filename(filespec)
-
     @classmethod
     def from_file_map(klass, file_map):
         raise NotImplementedError