Docs: Remove Library Model documentation

Library Model is deprecated, so remove the related description and
documentations.

Signed-off-by: Summer Qin <summer.qin@arm.com>
Change-Id: I3c9d1bba97c011183bea17bfd5ea7d9ec834802b
diff --git a/docs/technical_references/design_docs/source_structure.rst b/docs/technical_references/design_docs/source_structure.rst
index a42529e..89d7205 100644
--- a/docs/technical_references/design_docs/source_structure.rst
+++ b/docs/technical_references/design_docs/source_structure.rst
@@ -150,7 +150,6 @@
                                     such as the runtime API and the thread
                                     operation, etc.
 cmsis_psa/\*                        CMSIS implementation for PSA-FF-M SPM. [1]
-cmsis_func/\*                       The library model implementation. [2]
 \*                                  Implementation sources.
 =================================== ===========================================
 
@@ -162,4 +161,4 @@
 
 --------------
 
-*Copyright (c) 2020-2021, Arm Limited. All rights reserved.*
+*Copyright (c) 2020-2022, Arm Limited. All rights reserved.*