Fixes compile errors by moving files

The two files moved in this commit are referenced from the
javascript/lib qlpack, but they are located in the
javascript/src qlpack. This causes compile errors when running
compile-ish commands for javascript queries. Moving the
files fixes it.

javascript/ql/src/Declarations/UnusedProperty.ql

@@ -10,7 +10,7 @@
 
 import javascript
 import semmle.javascript.dataflow.LocalObjects
-import UnusedVariable
+import Declarations.UnusedVariable
 import UnusedParameter
 import Expressions.ExprHasNoEffect
 

javascript/ql/src/Declarations/UnusedVariable.ql

@@ -10,7 +10,7 @@
  */
 
 import javascript
-import UnusedVariable
+import Declarations.UnusedVariable
 
 /**
  * Holds if `v` is mentioned in a JSDoc comment in the same file, and that file

javascript/ql/src/Expressions/ExprHasNoEffect.ql

@@ -13,7 +13,7 @@
  */
 
 import javascript
-import ExprHasNoEffect
+import Expressions.ExprHasNoEffect
 import semmle.javascript.RestrictedLocations
 
 from Expr e

javascript/ql/src/Expressions/SelfAssignment.ql

@@ -12,7 +12,7 @@
  */
 
 import Clones
-import DOMProperties
+import Expressions.DOMProperties
 
 /**
  * Gets a description of expression `e`, which is assumed to be the left-hand

javascript/ql/src/LanguageFeatures/UnusedIndexVariable.ql

@@ -10,7 +10,7 @@
  */
 
 import javascript
-import UnusedIndexVariable
+import LanguageFeatures.UnusedIndexVariable
 
 from RelationalComparison rel, Variable idx, Variable v
 where unusedIndexVariable(rel, idx, v)