Remove compatibility patches needed when upgrading TO jQuery 1.x/2.x

[mgol]

Migrate 3.x still contains some patches for breaking changes in jQuery 1.9; it should only handle breaking changes in 3.0 or later. In Migrate 3.x, we'll leave it as-is, as removing patches would be a breaking change, but Migrate 4.0 should remove them.

[mgol]

This is done as part of #555. Note that we remove patches for breaking changes in 3.0 as well in that PR - a change from the previous plans.

[mgol]

Done in #555.