Uncouple integration tests from diktat, use simple script instead

[petertrr]

When we use a particular tool, like diktat, for testing SAVE, we need to spend a lot of time on version updates, fixing tests (#398, #407, #405), that sometimes lead to discovering bugs in the underlying tool. After Diktat will use SAVE for smoke testing (https://github.com/saveourtool/diktat/pull/1388), we can remove examples/kotlin-diktat from save-cli repo and use another tests tree with simple stubbing script instead of an actual tool.