(cherry picked from commit d743e52)
(cherry picked from commit 818b0df)
(cherry picked from commit 7b15e5e)

This reverts commit 1286d06.

# Conflicts:
#	openapi3filter/validation_discriminator_test.go

(cherry picked from commit a6bc0e1)
(cherry picked from commit 011aa82)

(cherry picked from commit 56c30a7)
(cherry picked from commit 393fdec)

(cherry picked from commit a3ea3ba)
(cherry picked from commit dfd1108)

(cherry picked from commit 1b40d29)
(cherry picked from commit f4f135f)

This reverts commit 9aa5c5a.

This is what schema.go:856 else is for

Spec quote:

    ``It is implied, that the property to which discriminator refers, contains the
    name of the target schema. In the example above, the objectType property should
    contain either simpleObject, or complexObject string.''*/