libstdc++: Fix Python deprecation warning in printers.py

python/libstdcxx/v6/printers.py:1355: DeprecationWarning: 'count' is passed as positional argument

The Python docs say:

  Deprecated since version 3.13: Passing count and flags as positional
  arguments is deprecated. In future Python versions they will be
  keyword-only parameters.

Using a keyword argument for count only became possible with Python 3.1
so introduce a new function to do the substitution.

libstdc++-v3/ChangeLog:

	* python/libstdcxx/v6/printers.py (strip_fundts_namespace): New.
	(StdExpAnyPrinter, StdExpOptionalPrinter): Use it.