Remove obsolete specification draft

See https://armmbed.github.io/mbed-crypto/psa/#hardware-abstraction-layer
instead.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/docs/.gitignore b/docs/.gitignore
index 33ae5ac..23f832b 100644
--- a/docs/.gitignore
+++ b/docs/.gitignore
@@ -1,3 +1,2 @@
 *.html
 *.pdf
-!PSACryptoDriverModelSpec.pdf
diff --git a/docs/PSACryptoDriverModelSpec.pdf b/docs/PSACryptoDriverModelSpec.pdf
deleted file mode 100644
index cf11380..0000000
--- a/docs/PSACryptoDriverModelSpec.pdf
+++ /dev/null
Binary files differ