unix: remove _SC_PAGESIZE on linux/sparc64

CL 62111 removed the _SC_PAGESIZE definition from the types_*.go files
but did not re-generate ztypes_linux_sparc64.go. Remove the definition
manually because linux/spar64 is not yet covered by the new Docker-based
build system.

Change-Id: I1ddebc3efa0d9d23c925ca84de31f63a3a883a99
Reviewed-on: https://go-review.googlesource.com/73876
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

unix/ztypes_linux_sparc64.go

@@ -652,8 +652,6 @@ type Sigset_t struct {
 	X__val [16]uint64
 }
 
-const _SC_PAGESIZE = 0x1e
-
 type Termios struct {
 	Iflag  uint32
 	Oflag  uint32