Remove solaris build tag and `contrib/mkimage/solaris

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Upstream-commit: 4785f1a7ab7ec857dc3ca849ee6ecadf519ef30e
Component: engine

components/engine/pkg/reexec/command_unix.go

@@ -1,4 +1,4 @@
-// +build freebsd solaris darwin
+// +build freebsd darwin
 
 package reexec
 

components/engine/pkg/reexec/command_unsupported.go

@@ -1,4 +1,4 @@
-// +build !linux,!windows,!freebsd,!solaris,!darwin
+// +build !linux,!windows,!freebsd,!darwin
 
 package reexec
 
@@ -6,7 +6,7 @@ import (
 	"os/exec"
 )
 
-// Command is unsupported on operating systems apart from Linux, Windows, Solaris and Darwin.
+// Command is unsupported on operating systems apart from Linux, Windows, and Darwin.
 func Command(args ...string) *exec.Cmd {
 	return nil
 }