Documentation: Remove all references of tips.html

The contents of tips.rst have been moved under usage.rst.
The mocking.rst still has a reference to tips.rst. Updated
it to usage.rst.

Change-Id: Ica3f482865bea0fe40cab47b6f2ee9795fd4f479
Signed-off-by: Sadiya Kazi <sadiyakazi@google.com>
diff --git a/mocking.rst b/mocking.rst
index 86d63f7..c73938b 100644
--- a/mocking.rst
+++ b/mocking.rst
@@ -224,7 +224,7 @@
 
 
 This pattern is generally useful and recommended `here
-<third_party/kernel/docs/tips.html#injecting-test-only-code>`__ for injecting
+<third_party/kernel/docs/usage.html#injecting-test-only-code>`__ for injecting
 other kinds of test-only code.
 
 .. note::
@@ -355,7 +355,7 @@
 - Won't work with tests built as modules.
 
 - More complicated, harder to understand, and less explicit.
-	
+
         - E.g. if you forgot to include the replacement definition in the
           compilation unit, the code will happily call the original one without
           any warning or indication.