Make 'is'-operator more stupid

Consider following expression: 'call() is Foo'. Suppose that we know
something about the 'call()', e.g. 'returns(foo) -> <condition>'

Previously, we've tried to re-use knowledge about 'call()', constructing
some smart clause, like 'returns(true) -> foo is Foo && <condition>'.

The conceptual error here is that *we can't* argue that <condition>
holds. Imagine that 'call()' actually has unspecified 'returns(foo2) ->
<!condition>', and 'foo2 is Foo' also holds. Then we would get
'returns(true) -> foo2 is Foo && <condition>' <=> 'returns(true) ->
<condition>' for the whole call, which is not correct.

More concrete example would be something like:
'if (!x.isNullOrEmpty() is Boolean)'

^KT-27241 Fixed

compiler/tests-spec/testData/diagnostics/notLinked/contracts/analysis/smartcasts/neg/15.kt

@@ -7,7 +7,6 @@
  * SECTIONS: contracts, analysis, smartcasts
  * NUMBER: 15
  * DESCRIPTION: Check smartcasts working if type checking for contract function is used
- * UNEXPECTED BEHAVIOUR
  * ISSUES: KT-27241
  */
 
@@ -40,20 +39,20 @@ import contracts.*
 // TESTCASE NUMBER: 1
 fun case_1(value: Any) {
     if (contracts.case_1_2(contracts.case_1_1(value is Char))) {
-        println(<!DEBUG_INFO_SMARTCAST!>value<!>.category)
+        println(value.<!UNRESOLVED_REFERENCE_WRONG_RECEIVER!>category<!>)
     }
 }
 
 // TESTCASE NUMBER: 2
 fun case_2(value: Any) {
     if (contracts.case_2(value is Char) is Boolean) {
-        println(<!DEBUG_INFO_SMARTCAST!>value<!>.category)
+        println(value.<!UNRESOLVED_REFERENCE_WRONG_RECEIVER!>category<!>)
     }
 }
 
 // TESTCASE NUMBER: 3
 fun case_3(value: String?) {
     if (<!USELESS_IS_CHECK!>!value.isNullOrEmpty() is Boolean<!>) {
-        <!DEBUG_INFO_SMARTCAST!>value<!>.length
+        value<!UNSAFE_CALL!>.<!>length
     }
 }