Doc: Removed TF-M prefix from document heading

This patch removes the TF-M/Trusted Firmware prefix from the
title heading across the documentation.

Change-Id: I60e0c6e48615f67ee040a0d6dbc7d6f1873856e7
Signed-off-by: Galanakis, Minos <minos.galanakis@arm.com>
diff --git a/docs/design_documents/tfm_its_service.rst b/docs/design_documents/tfm_its_service.rst
index 2de1e84..27f9300 100644
--- a/docs/design_documents/tfm_its_service.rst
+++ b/docs/design_documents/tfm_its_service.rst
@@ -1,6 +1,6 @@
-===========================================
-TF-M Internal Trusted Storage (ITS) Service
-===========================================
+======================================
+Internal Trusted Storage (ITS) Service
+======================================
 
 :Author: Jamie Fox
 :Organization: Arm Limited