What is the need for an inductor coil in a smps-buck converter?
The LC Combination as in the figure in question is a Low Pass filter. The inductor in addition to the capacitor is needed to filter the high frequency component of the output. Also, the inductor stores energy, so that once SW1 open up, then Inductor should store enough energy to flow a current through the diode(freewheeling). 
If you removed the inductor, then the diode will be reverse biased, and nothing will happen. Capacitor will just discharge to output.