Move contents of stdlib-jdk7/8 into stdlib

#KT-51907

libraries/stdlib/jdk7/build.gradle

@@ -11,7 +11,6 @@ configureJavadocJar()
 sourceSets {
     main {
         kotlin {
-            srcDir 'src'
         }
     }
     test {

libraries/stdlib/jdk7/java9/module-info.java

@@ -1,10 +1,4 @@
 @SuppressWarnings("module") // suppress warnings about terminal digit and exporting packages to not-yet-built kotlin-stdlib-jdk8
 module kotlin.stdlib.jdk7 {
     requires transitive kotlin.stdlib;
-
-    exports kotlin.jdk7;
-    exports kotlin.io.path;
-
-    exports kotlin.internal.jdk7 to kotlin.stdlib.jdk8;
-    opens kotlin.internal.jdk7 to kotlin.stdlib;
 }