Rename struct __res_params to res_params

The double-underscore prefixes are a leftover from when this code lived
in bionic. Now we're slowly getting rid of them...

Also cleanup transitive includes a bit.

Test: atest resolv_integration_test resolv_unit_test
Change-Id: I65ed8aed273be4af37a982a167f364a1f33f9a36
diff --git a/resolv/libnetd_resolv_test.cpp b/resolv/libnetd_resolv_test.cpp
index 2bd27fd..f4812a6 100644
--- a/resolv/libnetd_resolv_test.cpp
+++ b/resolv/libnetd_resolv_test.cpp
@@ -79,7 +79,7 @@
     }
 
     const char* mDefaultSearchDomains = "example.com";
-    const __res_params mDefaultParams_Binder = {
+    const res_params mDefaultParams_Binder = {
             .sample_validity = 300,
             .success_threshold = 25,
             .min_samples = 8,