vector: remove Go 1.8 support

This change reverts CL 32132. We no longer have to worry about
Go 1.5 support. This results in slightly simpler build constraints.

Change-Id: I021936646a6e9a82462a885b256894027fb58aeb
Reviewed-on: https://go-review.googlesource.com/c/148568
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/vector/acc_amd64.go b/vector/acc_amd64.go
index 68f6e03..cf535fc 100644
--- a/vector/acc_amd64.go
+++ b/vector/acc_amd64.go
@@ -4,7 +4,6 @@
 
 // +build !appengine
 // +build gc
-// +build go1.6
 // +build !noasm
 
 package vector
diff --git a/vector/acc_amd64.s b/vector/acc_amd64.s
index 6a424bc..69e0fc2 100644
--- a/vector/acc_amd64.s
+++ b/vector/acc_amd64.s
@@ -2,7 +2,6 @@
 
 // +build !appengine
 // +build gc
-// +build go1.6
 // +build !noasm
 
 #include "textflag.h"
diff --git a/vector/acc_other.go b/vector/acc_other.go
index 30425be..c98d20b 100644
--- a/vector/acc_other.go
+++ b/vector/acc_other.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64 appengine !gc !go1.6 noasm
+// +build !amd64 appengine !gc noasm
 
 package vector
 
diff --git a/vector/gen_acc_amd64.s.tmpl b/vector/gen_acc_amd64.s.tmpl
index 66b21a1..05ce25b 100644
--- a/vector/gen_acc_amd64.s.tmpl
+++ b/vector/gen_acc_amd64.s.tmpl
@@ -4,7 +4,6 @@
 
 // +build !appengine
 // +build gc
-// +build go1.6
 // +build !noasm
 
 #include "textflag.h"