all: remove unnecessary ", _" from map reads

If the bool value isn't used, there is no need to assign to underscore -
there is a shorter form that only returns the value and behaves in the
exact same way.

Change-Id: Iaf801b8e966da6c2f565bc39e3bb028175c92d60
Reviewed-on: https://go-review.googlesource.com/40920
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/go/types/api.go

@@ -245,7 +245,7 @@ func (info *Info) TypeOf(e ast.Expr) Type {
 // Precondition: the Uses and Defs maps are populated.
 //
 func (info *Info) ObjectOf(id *ast.Ident) Object {
-	if obj, _ := info.Defs[id]; obj != nil {
+	if obj := info.Defs[id]; obj != nil {
 		return obj
 	}
 	return info.Uses[id]

src/net/http/transport.go

@@ -805,7 +805,7 @@ func (t *Transport) removeIdleConnLocked(pconn *persistConn) {
 	}
 	t.idleLRU.remove(pconn)
 	key := pconn.cacheKey
-	pconns, _ := t.idleConn[key]
+	pconns := t.idleConn[key]
 	switch len(pconns) {
 	case 0:
 		// Nothing

src/net/internal/socktest/sys_cloexec.go

@@ -15,7 +15,7 @@ func (sw *Switch) Accept4(s, flags int) (ns int, sa syscall.Sockaddr, err error)
 		return syscall.Accept4(s, flags)
 	}
 	sw.fmu.RLock()
-	f, _ := sw.fltab[FilterAccept]
+	f := sw.fltab[FilterAccept]
 	sw.fmu.RUnlock()
 
 	af, err := f.apply(so)

src/net/internal/socktest/sys_unix.go

@@ -14,7 +14,7 @@ func (sw *Switch) Socket(family, sotype, proto int) (s int, err error) {
 
 	so := &Status{Cookie: cookie(family, sotype, proto)}
 	sw.fmu.RLock()
-	f, _ := sw.fltab[FilterSocket]
+	f := sw.fltab[FilterSocket]
 	sw.fmu.RUnlock()
 
 	af, err := f.apply(so)
@@ -47,7 +47,7 @@ func (sw *Switch) Close(s int) (err error) {
 		return syscall.Close(s)
 	}
 	sw.fmu.RLock()
-	f, _ := sw.fltab[FilterClose]
+	f := sw.fltab[FilterClose]
 	sw.fmu.RUnlock()
 
 	af, err := f.apply(so)
@@ -77,7 +77,7 @@ func (sw *Switch) Connect(s int, sa syscall.Sockaddr) (err error) {
 		return syscall.Connect(s, sa)
 	}
 	sw.fmu.RLock()
-	f, _ := sw.fltab[FilterConnect]
+	f := sw.fltab[FilterConnect]
 	sw.fmu.RUnlock()
 
 	af, err := f.apply(so)
@@ -106,7 +106,7 @@ func (sw *Switch) Listen(s, backlog int) (err error) {
 		return syscall.Listen(s, backlog)
 	}
 	sw.fmu.RLock()
-	f, _ := sw.fltab[FilterListen]
+	f := sw.fltab[FilterListen]
 	sw.fmu.RUnlock()
 
 	af, err := f.apply(so)
@@ -135,7 +135,7 @@ func (sw *Switch) Accept(s int) (ns int, sa syscall.Sockaddr, err error) {
 		return syscall.Accept(s)
 	}
 	sw.fmu.RLock()
-	f, _ := sw.fltab[FilterAccept]
+	f := sw.fltab[FilterAccept]
 	sw.fmu.RUnlock()
 
 	af, err := f.apply(so)
@@ -168,7 +168,7 @@ func (sw *Switch) GetsockoptInt(s, level, opt int) (soerr int, err error) {
 		return syscall.GetsockoptInt(s, level, opt)
 	}
 	sw.fmu.RLock()
-	f, _ := sw.fltab[FilterGetsockoptInt]
+	f := sw.fltab[FilterGetsockoptInt]
 	sw.fmu.RUnlock()
 
 	af, err := f.apply(so)