Removes a quantity of water for the specified APIUser, starting with the newest eligible entry and walking
backwards in time.

Eligible entries are identified by content: the intake must contain exactly one dish and that dish must be the
configured water class. This includes equivalent water-only entries created through /intake/manualInput/USERID.
Mixed intakes and fluids contributed by other food or drink classes are not targeted.

If timestamp is supplied, the operation considers entries from 00:00:00 on that local day through the supplied
time. Without it, the endpoint uses the target user's current local day through their current localized time.
quantity defaults to 250 ml.

Entries fully covered by the requested quantity are deactivated. If the final affected entry contains more water
than the remaining quantity, its serving size is reduced instead; at most one entry is partially edited. If less
water is available than requested, all available water is removed and the response reports the missing remainder.
Finding no eligible water is also a successful HTTP 200 response with removed: false.

This is a quantity-removal operation, not deletion of a fixed resource. Repeating an identical request removes
additional water from the then-current history. Use DELETE /intake/{imageId} to delete one known intake.