Don't count added labels when initializing slice (#10756)

This was added in #10749 but based on feedback it might be over-allocating so worth removing.

Signed-off-by: Łukasz Mierzwa <l.mierzwa@gmail.com>

model/labels/labels.go

@@ -452,7 +452,7 @@ func (b *Builder) Labels() Labels {
 
 	// In the general case, labels are removed, modified or moved
 	// rather than added.
-	res := make(Labels, 0, len(b.base)+len(b.add))
+	res := make(Labels, 0, len(b.base))
 Outer:
 	for _, l := range b.base {
 		for _, n := range b.del {