Skylark: Remove static type checking of variables/functions.

There are still some static checks (check existence of variable/function,
readonly variables, etc.). More cleanup will come later.

--
MOS_MIGRATED_REVID=90979748
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/AssignmentStatement.java b/src/main/java/com/google/devtools/build/lib/syntax/AssignmentStatement.java
index 601f128..6994231 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/AssignmentStatement.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/AssignmentStatement.java
@@ -63,6 +63,7 @@
 
   @Override
   void validate(ValidationEnvironment env) throws EvalException {
-    lvalue.validate(env, getLocation(), expression.validate(env));
+    expression.validate(env);
+    lvalue.validate(env, getLocation());
   }
 }