init: use FQName parse

FQName::FQName(string) could leave the FQName in an
invalid state, and so this constructor is being removed
and the mValid member is being removed.

Bug: 73774955
Test: boots + interface_start control messages received by init
Change-Id: I58d4a089c0a0f1c2cc5129c5e87321e7f6663b72
diff --git a/init/service.cpp b/init/service.cpp
index 8130e73..964393f 100644
--- a/init/service.cpp
+++ b/init/service.cpp
@@ -446,8 +446,8 @@
     const std::string& interface_name = args[1];
     const std::string& instance_name = args[2];
 
-    const FQName fq_name = FQName(interface_name);
-    if (!fq_name.isValid()) {
+    FQName fq_name;
+    if (!FQName::parse(interface_name, &fq_name)) {
         return Error() << "Invalid fully-qualified name for interface '" << interface_name << "'";
     }