Remove unnecessary comma.

Doc/lib/libcmath.tex

@@ -83,7 +83,7 @@ The mathematical constant \emph{e}, as a real.
 
 Note that the selection of functions is similar, but not identical, to
 that in module \refmodule{math}\refbimodindex{math}.  The reason for having
-two modules is, that some users aren't interested in complex numbers,
+two modules is that some users aren't interested in complex numbers,
 and perhaps don't even know what they are.  They would rather have
 \code{math.sqrt(-1)} raise an exception than return a complex number.
 Also note that the functions defined in \module{cmath} always return a