pkg/proc: do not check decl line for FunctionArguments (#3254)

Fixes a bug where we cannot get locals (including arguments and return
values) from a given scope because the line number state machine ends up
in an invalid state because of this parameter being set to false.

_fixtures/traceprog.go

@@ -0,0 +1,13 @@
+package main
+
+import "fmt"
+
+func callme(i int) int {
+	return i * i
+}
+
+func main() {
+	j := 0
+	j += callme(2)
+	fmt.Println(j)
+}