(#5566) Treat source only File checksums as syntax errors when used with content

Certain checksum types (ctime, mtime) only make sense when used with the
'source' File parameter, since there is no way to check them on raw
strings.

Given the limitations of the current checksumming implementations, it is
likely to introduce unexpected behavior when using the 'none' checksum
type and either one of the 'source', and 'content' File parameters.
Because of this, it is now a syntax error to use a checksum of 'none' with
either parameter.

Paired-with: Jesse Wolfe <jesse@puppetlabs.com>