Remove confusing <//>

[ringabout]

Ref #15307

[timotheecour]

I'm assuming this is possible thanks to csources being updated (refs #16282) to 1.0.11 ?

can these be removed too?

lib/system.nim:889:13:  template `<//>`*(t: untyped): untyped = owned(t)
lib/system.nim:912:13:  template `<//>`*(t: untyped): untyped = t

if for some reason they can't, then how about hiding it behind -d:nimLegacyOwnedOperator

[ringabout]

I'm assuming this is possible thanks to csources being updated (refs #16282) to 1.0.11 ?

Yeah

if for some reason they can't, then how about hiding it behind -d:nimLegacyOwnedOperator

Ok, let me try to remove it. It should migrate easily even if it's breaking changes. And I guess nobody used it. It looks scary :)

[ringabout]

only fusion/btreetables.nim failed, so I made an associated PR
nim-lang/fusion#90