rm no-updirs and case-tolerant, add no-parent-or-current-test

Method case-tolerant moved to File::Spec::Case (which is already working).

Method no-updirs looked like something that you'd run on the output of perl5  `@dirs = readdir DIRHANDLE;`.  Since that's not how we're doing things in P6, it should be in the form of a test passed to dir().

It got the long name no-parent-or-current-test because "no-updirs" already didn't do what I expected it to do from the name.  Ironically, the long function name has the terse code:  `none('.', '..')`.