Removed remains of deprecated function ss2tf

Author: olof3

README.md

@@ -73,7 +73,7 @@ A documentation website is available at [http://juliacontrol.github.io/ControlSy
 
 Some of the available commands are:
 ##### Constructing systems
-ss, tf, zpk, ss2tf
+ss, tf, zpk
 ##### Analysis
 pole, tzero, norm, hinfnorm, linfnorm, ctrb, obsv, gangoffour, margin, markovparam, damp, dampreport, zpkdata, dcgain, covar, gram, sigma, sisomargin
 ##### Synthesis

src/ControlSystems.jl

@@ -9,7 +9,6 @@ export  LTISystem,
         ss,
         tf,
         zpk,
-        ss2tf,
         LQG,
         isproper,
         # Linear Algebra

test/test_conversion.jl

@@ -94,7 +94,7 @@ G2 = tf([1,1,-1],[1,0,-1])
 sys3 = ss([0 1;1 0],[0;1],[1 1],0)
 G3 = tf([1,1],[1,0,-1])
 
-#Test ss2tf
+#Test conversion of StateSpace to TransferFunction
 @test tf(sys2) ≈ G2 atol=1e-15
 @test tf(sys3) ≈ G3 atol=1e-15