tests: fix memory leaks (#2389)

packages/snjs/mocha/vaults/signatures.test.js

@@ -9,11 +9,6 @@ describe('signatures', function () {
 
   let context
 
-  afterEach(async function () {
-    await context.deinit()
-    localStorage.clear()
-  })
-
   beforeEach(async function () {
     localStorage.clear()
 
@@ -23,6 +18,13 @@ describe('signatures', function () {
     await context.register()
   })
 
+  afterEach(async function () {
+    await context.deinit()
+    localStorage.clear()
+    sinon.restore()
+    context = undefined
+  })
+
   describe('item decryption signature verification', () => {
     it('should have failing signature if contact public key does not match', async () => {
       const { note, contactContext, deinitContactContext } =