Fix some warnings about string-delete and string-filter argument order

Fix some warnings about string-delete and  string-filter argument order

This makes guile2 stop printing some warning messages:

  Guile used to use the wrong argument order for string-delete.
  This call to string-filter had the arguments in the wrong order.
  See SRFI-13 for more details. At some point we will remove this hack.

guile-1.8 will continue working.