TBR: v.io/jiri/profiles: FindTarget == FindTargetWithDefault

Before this CL, FindTarget == FindTargetWithDefault, which seems
incorrect.  In particular, it was causing:

EnsureProfileTargetIsInstalled(..., "amd64-linux")

to succeed, even though the "arm-android" profile was installed.

Change-Id: I01896acffaa4b23d2b91892061079412bb9e075e
diff --git a/profiles/env_test.go b/profiles/env_test.go
index 535bfdd..f057c3c 100644
--- a/profiles/env_test.go
+++ b/profiles/env_test.go
@@ -32,7 +32,10 @@
 	}
 	ch.Vars = envvar.VarsFromOS()
 	ch.Delete("CGO_CFLAGS")
-	native, _ := profiles.NewTarget("native")
+	native, err := profiles.NewTarget("amd64-darwin")
+	if err != nil {
+		t.Fatal(err)
+	}
 	ch.MergeEnvFromProfiles(profiles.JiriMergePolicies(), native, "go", "syncbase")
 	if got, want := ch.Get("CGO_CFLAGS"), "-IX -IY -IA -IB"; got != want {
 		t.Errorf("got %v, want %v", got, want)
@@ -66,7 +69,10 @@
 		t.Fatal(err)
 	}
 	ch.Vars = envvar.VarsFromSlice([]string{})
-	t1Target, _ := profiles.NewTarget("cpu1-os1@1")
+	t1Target, err := profiles.NewTarget("cpu1-os1@1")
+	if err != nil {
+		t.Fatal(err)
+	}
 	ch.MergeEnvFromProfiles(map[string]profiles.MergePolicy{
 		"A": profiles.AppendFlag,
 		"B": profiles.UseLast,
diff --git a/profiles/target.go b/profiles/target.go
index cffcbd9..5bf831c 100644
--- a/profiles/target.go
+++ b/profiles/target.go
@@ -323,10 +323,6 @@
 // only a single target available in targets then that one target is considered
 // as matching.
 func FindTarget(targets OrderedTargets, target *Target) *Target {
-	if len(targets) == 1 && !target.IsSet() {
-		tmp := *targets[0]
-		return &tmp
-	}
 	for _, t := range targets {
 		if target.Match(t) {
 			tmp := *t