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/DnsTlsSocket.cpp b/server/dns/DnsTlsSocket.cpp
index 8e25b1f..df48d91 100644
--- a/server/dns/DnsTlsSocket.cpp
+++ b/server/dns/DnsTlsSocket.cpp
@@ -132,7 +132,7 @@
 bool DnsTlsSocket::initialize() {
     // This method should only be called once, at the beginning, so locking should be
     // unnecessary.  This lock only serves to help catch bugs in code that calls this method.
-    std::lock_guard<std::mutex> guard(mLock);
+    std::lock_guard guard(mLock);
     if (mSslCtx) {
         // This is a bug in the caller.
         return false;
@@ -340,7 +340,7 @@
 }
 
 void DnsTlsSocket::loop() {
-    std::lock_guard<std::mutex> guard(mLock);
+    std::lock_guard guard(mLock);
     // Buffer at most one query.
     Query q;
 
@@ -413,7 +413,7 @@
     mIpcInFd.reset();
     {
         // Wait for the orderly shutdown to complete.
-        std::lock_guard<std::mutex> guard(mLock);
+        std::lock_guard guard(mLock);
         if (mLoopThread && std::this_thread::get_id() == mLoopThread->get_id()) {
             ALOGE("Violation of re-entrance precondition");
             return;