Drop detecting cudaMemcpyPeer

it seems CUDA 9.0 changed the symbol appearance, just assume it is there by default

configure.ac

@@ -1377,14 +1377,7 @@ fi
 # Peer transfers are only supported since CUDA 4.0
 # Disable them if user explicity wants to disable them
 AC_ARG_ENABLE(cuda_memcpy_peer, [AS_HELP_STRING([--disable-cuda-memcpy-peer], [do not allow peer transfers when using CUDA 4.0])],, [enable_cuda_memcpy_peer=yes])
-have_cuda_memcpy_peer=no
-if test x$enable_cuda_memcpy_peer = xyes -a x$enable_cuda = xyes ; then
-    SAVED_LDFLAGS="${LDFLAGS}"
-    LDFLAGS="${LDFLAGS} ${STARPU_CUDA_LDFLAGS}"
-    AC_CHECK_FUNC([cudaMemcpyPeer], have_cuda_memcpy_peer=yes, have_cuda_memcpy_peer=no)
-    LDFLAGS="${SAVED_LDFLAGS}"
-fi
-if test x$have_cuda_memcpy_peer = xyes; then
+if test x$enable_cuda_memcpy_peer = xyes; then
     AC_DEFINE(STARPU_HAVE_CUDA_MEMCPY_PEER,[1],[Peer transfers are supported in CUDA])
 fi