fold parseLinkTarget into parseLinkTargetOrPointer

fold parseLinkTarget into parseLinkTargetOrPointer

Only one place remained that differentiated between them.

It is the case that a symlink target that happens to contain a newline
somehow will be treated as a link to a key truncated at the newline.
This is super unlikely to happen, and since a key cannot actually
contain a newline, it's as good a behavior as any. Anyway, this commit
does not change the behavior there, although arguably it should be
changed. Note that getAnnexLinkTarget does prevent a symlink target
containing a newline.

Sponsored-by: Dartmouth College's Datalad project