runtime: remove unused SYS_* definitions on Linux

Also fix the indentation of the SYS_* definitions in sys_linux_mipsx.s
and order them numerically.

Change-Id: I0c454301c329a163e7db09dcb25d4e825149858c
Reviewed-on: https://go-review.googlesource.com/98448
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/sys_linux_arm.s

@@ -23,7 +23,6 @@
 #define SYS_close (SYS_BASE + 6)
 #define SYS_getpid (SYS_BASE + 20)
 #define SYS_kill (SYS_BASE + 37)
-#define SYS_gettimeofday (SYS_BASE + 78)
 #define SYS_clone (SYS_BASE + 120)
 #define SYS_rt_sigreturn (SYS_BASE + 173)
 #define SYS_rt_sigaction (SYS_BASE + 174)

src/runtime/sys_linux_arm64.s

@@ -18,7 +18,6 @@
 #define SYS_openat		56
 #define SYS_close		57
 #define SYS_fcntl		25
-#define SYS_gettimeofday	169
 #define SYS_pselect6		72
 #define SYS_mmap		222
 #define SYS_munmap		215

src/runtime/sys_linux_mips64x.s

@@ -22,7 +22,6 @@
 #define SYS_getpid		5038
 #define SYS_kill		5060
 #define SYS_fcntl		5080
-#define SYS_gettimeofday	5094
 #define SYS_mmap		5009
 #define SYS_munmap		5011
 #define SYS_setitimer		5036

src/runtime/sys_linux_mipsx.s

@@ -20,8 +20,8 @@
 #define SYS_close		4006
 #define SYS_getpid		4020
 #define SYS_kill		4037
+#define SYS_brk			4045
 #define SYS_fcntl		4055
-#define SYS_gettimeofday	    4078
 #define SYS_mmap		4090
 #define SYS_munmap		4091
 #define SYS_setitimer		4104
@@ -44,7 +44,6 @@
 #define SYS_epoll_wait		4250
 #define SYS_clock_gettime	4263
 #define SYS_epoll_create1	4326
-#define SYS_brk			    4045
 
 TEXT runtime·exit(SB),NOSPLIT,$0-4
 	MOVW	code+0(FP), R4

src/runtime/sys_linux_ppc64x.s

@@ -23,8 +23,6 @@
 #define SYS_kill		 37
 #define SYS_brk			 45
 #define SYS_fcntl		 55
-#define SYS_gettimeofday	 78
-#define SYS_select		 82	// always return -ENOSYS
 #define SYS_mmap		 90
 #define SYS_munmap		 91
 #define SYS_setitimer		104

src/runtime/sys_linux_s390x.s

@@ -18,7 +18,6 @@
 #define SYS_kill                 37
 #define SYS_brk			 45
 #define SYS_fcntl                55
-#define SYS_gettimeofday         78
 #define SYS_mmap                 90
 #define SYS_munmap               91
 #define SYS_setitimer           104