doc: Remove ssl as a required dependency from build-unix

doc/build-unix.md

@@ -33,7 +33,6 @@ These dependencies are required:
 
  Library     | Purpose          | Description
  ------------|------------------|----------------------
- libssl      | Crypto           | Random Number Generation, Elliptic Curve Cryptography
  libboost    | Utility          | Library for threading, data structures, etc
  libevent    | Networking       | OS independent asynchronous networking
 
@@ -81,7 +80,7 @@ Build requirements:
 
 Now, you can either build from self-compiled [depends](/depends/README.md) or install the required dependencies:
 
-    sudo apt-get install libssl-dev libevent-dev libboost-system-dev libboost-filesystem-dev libboost-chrono-dev libboost-test-dev libboost-thread-dev
+    sudo apt-get install libevent-dev libboost-system-dev libboost-filesystem-dev libboost-chrono-dev libboost-test-dev libboost-thread-dev
 
 BerkeleyDB is required for the wallet.