cmd/syncthing: Enable KCP by default

Also, use upstream library, as my changes have been merged.

vendor/github.com/klauspost/reedsolomon/galois_noasm.go

@@ -1,19 +0,0 @@
-//+build !amd64 noasm appengine
-
-// Copyright 2015, Klaus Post, see LICENSE for details.
-
-package reedsolomon
-
-func galMulSlice(c byte, in, out []byte, ssse3, avx2 bool) {
-	mt := mulTable[c]
-	for n, input := range in {
-		out[n] = mt[input]
-	}
-}
-
-func galMulSliceXor(c byte, in, out []byte, ssse3, avx2 bool) {
-	mt := mulTable[c]
-	for n, input := range in {
-		out[n] ^= mt[input]
-	}
-}