debug/plan9obj: simplify s[:] to s where

Change-Id: Ib2eee1215ba046e4541af8afa3a921c680d2b37e
Reviewed-on: https://go-review.googlesource.com/c/142037
Run-TryBot: Iskander Sharipov <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Iskander Sharipov <[email protected]>

Author: OlgaVlPetrova

plan9obj/file.go

@@ -274,7 +274,7 @@ func newTable(symtab []byte, ptrsz int) ([]Sym, error) {
 		ts.Value = s.value
 		switch s.typ {
 		default:
-			ts.Name = string(s.name[:])
+			ts.Name = string(s.name)
 		case 'z', 'Z':
 			for i := 0; i < len(s.name); i += 2 {
 				eltIdx := binary.BigEndian.Uint16(s.name[i : i+2])