doc: Remove outdated qt4 install information from README.md

This text is aimed at users installing the binaries.

Now that Qt5 is linked statically, there is no need to install Qt
as a run-time dependency.

Author: laanwj

doc/README.md

@@ -11,17 +11,11 @@ The following are some helpful notes on how to run Bitcoin on your native platfo
 
 ### Unix
 
-You need the Qt4 run-time libraries to run Bitcoin-Qt. On Debian or Ubuntu:
-
-	sudo apt-get install libqtgui4
-
 Unpack the files into a directory and run:
 
 - bin/32/bitcoin-qt (GUI, 32-bit) or bin/32/bitcoind (headless, 32-bit)
 - bin/64/bitcoin-qt (GUI, 64-bit) or bin/64/bitcoind (headless, 64-bit)
 
-
-
 ### Windows
 
 Unpack the files into a directory, and then run bitcoin-qt.exe.