security+tools: deprecate TPM unlock functionality

And remove the implementation in the tpm-osxkeychain backend

Refs: #4754
Change-Id: I6d61b7aab83aba2c9128b524e178c71de8635b75
diff --git a/docs/manpages/ndnsec-unlock-tpm.rst b/docs/manpages/ndnsec-unlock-tpm.rst
index 5e18108..858f0b6 100644
--- a/docs/manpages/ndnsec-unlock-tpm.rst
+++ b/docs/manpages/ndnsec-unlock-tpm.rst
@@ -9,5 +9,7 @@
 Description
 -----------
 
+**DEPRECATED**
+
 This command can be used to (temporarily) unlock the local
 **Trusted Platform Module (TPM)** that manages the private keys.