Let lock_guard deduce its template argument

No functional change, this is a cleanup.

With C++17, it's no longer necessary to specify the teplate argument
when it can be deduced from the types of constructor arguments. This
allows de-cluttering our locking statements.

To avoid typos, this patch was mechanically generated:

  perl -p -i -e 's/std::lock_guard<std::mutex>/std::lock_guard/g' \
    $(find . -name '*.cpp' -o -name '*.h')

Change-Id: Ibb15d9a6c5b1c861d81353e47d25474eb1d4c2df
diff --git a/server/dns/DnsTlsTransport.cpp b/server/dns/DnsTlsTransport.cpp
index 033ae80..e94daff 100644
--- a/server/dns/DnsTlsTransport.cpp
+++ b/server/dns/DnsTlsTransport.cpp
@@ -36,7 +36,7 @@
 namespace net {
 
 std::future<DnsTlsTransport::Result> DnsTlsTransport::query(const netdutils::Slice query) {
-    std::lock_guard<std::mutex> guard(mLock);
+    std::lock_guard guard(mLock);
 
     auto record = mQueries.recordQuery(query);
     if (!record) {
@@ -89,7 +89,7 @@
 }
 
 void DnsTlsTransport::onClosed() {
-    std::lock_guard<std::mutex> guard(mLock);
+    std::lock_guard guard(mLock);
     if (mClosing) {
         return;
     }
@@ -109,7 +109,7 @@
 }
 
 void DnsTlsTransport::doReconnect() {
-    std::lock_guard<std::mutex> guard(mLock);
+    std::lock_guard guard(mLock);
     if (mClosing) {
         return;
     }
@@ -126,7 +126,7 @@
 DnsTlsTransport::~DnsTlsTransport() {
     ALOGV("Destructor");
     {
-        std::lock_guard<std::mutex> guard(mLock);
+        std::lock_guard guard(mLock);
         ALOGV("Locked destruction procedure");
         mQueries.clear();
         mClosing = true;