Incompatibilities 2019: document removal of "com.yourkit" package.

reference_guide/api_changes/api_changes_list_2019.md

@@ -17,6 +17,9 @@ See the note on how to document new problems on the main page reference_guide/ap
 `com.intellij.ui.layout.Cell.invoke$default(Cell, JComponent, CCFlags[], int, GrowPolicy, String, int, Object)` method parameter type changed
 : Signature of this function has been seriously changed without possibility to keep the old function. Change invocations and overriding of that function according to new parameters and recompile the code. 
 
+`com.yourkit` package removed
+: YourKit library has been extracted into the separate plugin which is not bundled in all IDEs by default. YourKit library is a library for profiling IDE, and its util classes shouldn't be used for general purpose. Instead of `com.yourkit.util.Strings` please use  `org.apache.commons.lang.StringUtils`.  Instead of `com.yourkit.util.ArrayUtil` please use `org.apache.commons.lang.ArrayUtils`
+
 ## Changes in IntelliJ Platform 2019.1
 
 `kotlinx.coroutines.experimental` package removed