syscall: replace zsyscall_windows_*.go files with a single file

zsyscall_windows_386.go and zsyscall_windows_amd64.go contain same bytes

LGTM=r
R=golang-codereviews, r
CC=golang-codereviews
https://golang.org/cl/124640043

src/pkg/syscall/mkall.sh

@@ -244,7 +244,7 @@ esac
 	case "$GOOS" in
 	windows)
 		echo "GOOS= GOARCH= go build mksyscall_windows.go"
-		echo "./mksyscall_windows syscall_windows.go security_windows.go syscall_$GOOSARCH.go |gofmt >zsyscall_$GOOSARCH.go"
+		echo "./mksyscall_windows syscall_windows.go security_windows.go |gofmt >zsyscall_windows.go"
 		echo "rm -f ./mksyscall_windows"
 		;;
 	*)

src/pkg/syscall/mkall_windows.bat

@@ -8,14 +8,8 @@ echo mkall_windows.bat must be run from src\pkg\syscall directory
 goto :end
 :dirok
 
-if "%1"=="386" goto :paramok
-if "%1"=="amd64" goto :paramok
-echo parameters must be 386 or amd64
-goto :end
-:paramok
-
 go build mksyscall_windows.go
-.\mksyscall_windows syscall_windows.go security_windows.go syscall_windows_%1.go |gofmt >zsyscall_windows_%1.go
+.\mksyscall_windows syscall_windows.go security_windows.go |gofmt >zsyscall_windows.go
 del mksyscall_windows.exe
 
-:end
\ No newline at end of file
+:end