Remove documentation of "val-or-fail"

This is an untested documentation detail of val() processing and
a hack to use the same code for numerification of strings.

Author: lizmat

doc/Type/Str.pod6

@@ -1113,15 +1113,13 @@ Throws C<X::Cannot::Capture>.
 
 =head2 routine val
 
-    multi sub val(Str:D $MAYBEVAL, :$val-or-fail)
+    multi sub val(Str:D $MAYBEVAL)
 
 Given a C<Str> that may be parsable as a numeric value, it will
 attempt to construct the appropriate L<allomorph|/language/glossary#Allomorph>,
 returning one of L<IntStr|/type/IntStr>, L<NumStr|/type/NumStr>, L<RatStr|/type/RatStr>
 or L<ComplexStr|/type/ComplexStr> or a plain C<Str> if a numeric value cannot
-be parsed.  If the C<:val-or-fail> adverb is provided it will return an
-L<X::Str::Numeric|/type/X::Str::Numeric> rather than the original string if it
-cannot parse the string as a number.
+be parsed.
 
     say val("42").^name;    # OUTPUT: «IntStr␤»
     say val("42e0").^name;  # OUTPUT: «NumStr␤»