check: simplify code via DeleteSyntheticNodes

We had multiple pieces of code to deal with ssa's generated calls, such
as the one needed when a non-pointer method is called on a pointer
receiver.

Instead, use DeleteSyntheticNodes, which gets rid of those and "inlines"
these now removed edges. That means we no longer have to worry about
these edge cases.

The proof is that the tests still pass, and there are no changes to the
warnings emitted for all of std cmd.

check/check.go

@@ -178,6 +178,7 @@ func (c *Checker) Check() ([]lint.Issue, error) {
 	default:
 		return nil, fmt.Errorf("unknown call graph construction algorithm: %q", c.algo)
 	}
+	cg.DeleteSyntheticNodes()
 
 	var issues []lint.Issue
 funcLoop:
@@ -222,16 +223,6 @@ funcLoop:
 				c.debug("  skip - type is required via call\n")
 				continue funcLoop
 			}
-			caller := edge.Caller.Func
-			switch {
-			case len(caller.FreeVars) == 1 && strings.HasSuffix(caller.Name(), "$bound"):
-				// passing method via someFunc(type.method)
-				fallthrough
-			case len(caller.FreeVars) == 0 && strings.HasSuffix(caller.Name(), "$thunk"):
-				// passing method via someFunc(recv.method)
-				c.debug("  skip - type is required via call\n")
-				continue funcLoop
-			}
 			switch edge.Site.Common().Value.(type) {
 			case *ssa.Function:
 			default:
@@ -416,9 +407,6 @@ func mainPackages(prog *ssa.Program, wantPkg map[*types.Package]*loader.PackageI
 
 func calledInReturn(calls []*callgraph.Edge) bool {
 	for _, edge := range calls {
-		if edge.Pos() == token.NoPos { // generated call
-			continue
-		}
 		val := edge.Site.Value()
 		if val == nil { // e.g. go statement
 			continue
@@ -648,9 +636,6 @@ func (c *Checker) multipleImpls(info *loader.PackageInfo, fn *ssa.Function) bool
 		return false
 	}
 	path := c.prog.Fset.Position(fn.Pos()).Filename
-	if path == "" { // generated func, like init
-		return false
-	}
 	count := c.declCounts(filepath.Dir(path), info.Pkg.Name())
 	name := fn.Name()
 	if fn.Signature.Recv() != nil {