dirvers/btrfs: remove btrfs_noversion tag

The header should be included since btrfs-progs 3.16.1, it is over 10
years old now so I think we can just drop the tag and assume it is
always there. This allows us to simplify the buildtag script as well.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

storage/drivers/btrfs/version.go

@@ -1,4 +1,4 @@
-//go:build linux && !btrfs_noversion && cgo
+//go:build linux && cgo
 
 package btrfs
 

storage/drivers/btrfs/version_none.go

@@ -1,14 +0,0 @@
-//go:build linux && btrfs_noversion && cgo
-
-package btrfs
-
-// TODO(vbatts) remove this work-around once supported linux distros are on
-// btrfs utilities of >= 3.16.1
-
-func btrfsBuildVersion() string {
-	return "-"
-}
-
-func btrfsLibVersion() int {
-	return -1
-}

storage/drivers/btrfs/version_test.go

@@ -1,4 +1,4 @@
-//go:build linux && !btrfs_noversion && cgo
+//go:build linux && cgo
 
 package btrfs
 

storage/hack/btrfs_tag.sh

@@ -7,11 +7,4 @@ cc -E - >/dev/null 2>/dev/null <<-EOF
 EOF
 if test $? -ne 0; then
     echo exclude_graphdriver_btrfs
-else
-    cc -E - >/dev/null 2>/dev/null <<-EOF
-	#include <btrfs/version.h>
-	EOF
-    if test $? -ne 0; then
-        echo btrfs_noversion
-    fi
 fi