Remove unused rule for "cvectorcmatrix" from Makefile.am.

@Markus: You have committed this rule beginning of August (and briefly removed
         it mid of August), but AFAICT you never committed
         "cvectorcmatrix.cc".  If you still have that file somewhere, can you
         please commit it and reinstate this rule?

[[Imported from SVN: r1298]]

dune/istl/test/Makefile.am

@@ -66,8 +66,6 @@ iotest_SOURCES = iotest.cc
 
 scaledidmatrixtest_SOURCES = scaledidmatrixtest.cc
 
-cvectorcmatrix_SOURCES = cvectorcmatrix.cc
-
 if MPI
   indicestest_SOURCES = indicestest.cc
   indicestest_CPPFLAGS = $(AM_CPPFLAGS)		\