[RFD] Revert "Match Swarm in how to combine filters"

[thaJeztah]

When filtering objects on labels, and two different filter values
are passed for a single label, Swarm combines those filters as
an AND. Effectively, this means that:

--filter label=something=yes
--filter label=something=no

Means;

Give me all objects that have label "something" set to "yes AND no"

This is never true, because labels are stored as a "map" (so an
object can only have a single label named "something". As
a result this filter will never return a result.

This behavior is also inconsistent with other situations, where
filters are combined using an OR, for example;

--filter label=something=yes
--filter label=somethingelse=foo

Means;

Give me all objects that have label "something" set to "yes",
and/or label "somethingelse" set to "foo"

This commit was added to make Kubernetes mimic the (odd) behavior,
so that the behavior would be consistent for both orchestrators.

Given that the existing (swarm/docker) behavior;

• Is an oversight (bug?)
• Is not (clearly) documented
• Most likely a very narrow corner-case

It may be a better option to fix the situation in the Swarm side
(if desirable, keep the old behavior based on API version), and
revert this commit to not let this behavior find its way into
new features.

This reverts commit 297866e (#1023).