[ZEPPELIN-5982] Merge flink-scala-parent module into flink-scala-2.12 (…

…#4694)

* [ZEPPELIN-5982] Merge flink-scala-parent module into flink-scala-2.12

flink/README.md

@@ -6,25 +6,21 @@ This is the doc for Zeppelin developers who want to work on flink interpreter.
 
 ### Project Structure
 
-Flink interpreter is more complex than other interpreter (such as jdbc, shell). Currently it has following 8 modules
+Flink interpreter is more complex than other interpreter (such as jdbc, shell).
+Currently, it has the following modules clustered into two groups:
+
 * flink-shims
 * flink1.15-shims
 * flink1.16-shims
 * flink1.17-shims
-* flink-scala-parent
+
 * flink-scala-2.12
 
-The first 4 modules are to adapt different flink versions because there're some api changes between different versions of flink.
+The modules in the first group are to adapt different flink versions because there're some api changes between different versions of flink.
 `flink-shims` is parent module for other shims modules. 
 At runtime Flink interpreter will load the FlinkShims based on the current flink versions (See `FlinkShims#loadShims`). 
 
-The remaining 2 modules are to adapt different scala versions (Apache Flink only supports Scala 2.12).
-`flink-scala-parent` is a parent module for `flink-scala-2.12`.
-There's symlink folder `flink-scala-parent` under `flink-scala-2.12`.
-When you run maven command to build flink interpreter, the source code in `flink-scala-parent` won't be compiled directly, instead
-they will be compiled against different scala versions when building `flink-scala-2.12`. (See `build-helper-maven-plugin` in `pom.xml`)
-Both `flink-scala-2.12` build a flink interpreter jar and `FlinkInterpreterLauncher` in `zeppelin-plugins/launcher/flink` will choose the right jar based
-on the scala version of flink.
+The modules in the second group are to adapt different scala versions. But since flink 1.15, it only supports Scala 2.12, thus there is only one module `flink-scala-2.12`
 
 ### Work in IDE