Remove the crypto submodule

All crypto files are now in the main tree.
diff --git a/.gitmodules b/.gitmodules
deleted file mode 100644
index 33ccb13..0000000
--- a/.gitmodules
+++ /dev/null
@@ -1,4 +0,0 @@
-[submodule "crypto"]
-	path = crypto
-	url = https://github.com/ARMmbed/mbed-crypto
-	branch = development
diff --git a/crypto b/crypto
deleted file mode 160000
index cf4a40b..0000000
--- a/crypto
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit cf4a40ba0a3086cabb5a8227245191161fd26383