doc: remove Boost Chrono from install docs

Author: fanquake

doc/build-unix.md

@@ -80,7 +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 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-test-dev libboost-thread-dev
 
 BerkeleyDB is required for the wallet.