doc: clean up references to `Tracking Locations'.

doc: clean up references to `Tracking Locations'.

* doc/bison.texinfo (Locations): Rename node to...
(Tracking Locations): ... this, which is its section name, and
update all cross references.  The trouble is that there is another
node about locations.  Its section name is `Locations', which was
easily confused with the node name of this node.  Moreover, its
node name is `Locations Overview', which was mistakenly used to
label some cross references to this node.