Python: Revert "Python: Support moduleImport("dotted.name") in API graphs"

This reverts commit 2c4a477.

It's probably best _not_ to do this, as any `getMember` cycle in the
API graph will lead to nontermination.

Author: tausbn

python/ql/src/semmle/python/ApiGraphs.qll

@@ -209,14 +209,12 @@ module API {
 
   /**
    * Gets a node corresponding to an import of module `m`.
+   *
+   * Note: You should only use this predicate for top level modules. If you want nodes corresponding to a submodule,
+   * you should use `.getMember` on the parent module. For example, for nodes corresponding to the module `foo.bar`,
+   * use `moduleImport("foo").getMember("bar")`.
    */
-  Node moduleImport(string m) {
-    result = Impl::MkModuleImport(m)
-    or
-    exists(string before_dot, string after_dot | before_dot + "." + after_dot = m |
-      result = moduleImport(before_dot).getMember(after_dot)
-    )
-  }
+  Node moduleImport(string m) { result = Impl::MkModuleImport(m) }
 
   /**
    * Provides the actual implementation of API graphs, cached for performance.