this change tries to reduce the number of callers using operator<<()
for printing UUID. they are found by compiling the tree after commenting
out `operator<<(std::ostream& out, const UUID& uuid)`. but this change
alone is not enough to drop all callers, as some callers are using
`operator<<(ostream&, const unordered_map&)` and other overloads to
print ranges whose elements contain UUID. so in order to limit the
scope of the change, we are not changing them here.
Refs #13245
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
94c6df0a08