closeSession: actually remove elements from sessions_

std::remove_if consolidates the non-removed elements at the start of
the vector, but it doesn't change the vector's size. After upgrading
libc++, std::remove_if is [[nodiscard]], so this bug causes a compiler
error.

Bug: 175635923
Test: m android.hardware.drm-service.castkey
Change-Id: Ie9734e616f0f93e290cd61f929af04598f236ee7

cast_auth/mediadrm/SessionLibrary.cpp

@@ -29,10 +29,11 @@ std::vector<uint8_t> SessionLibrary::createSession() {
 
 void SessionLibrary::closeSession(const std::vector<uint8_t>& session) {
     std::lock_guard<std::mutex> guard(session_lock_);
-    std::remove_if(sessions_.begin(), sessions_.end(),
-                   [&session](const std::vector<uint8_t>& e) {
-                     return std::equal(e.begin(), e.end(), session.begin());
-                   });
+    sessions_.erase(std::remove_if(sessions_.begin(), sessions_.end(),
+                                   [&session](const std::vector<uint8_t>& e) {
+                                     return std::equal(e.begin(), e.end(), session.begin());
+                                   }),
+                    sessions_.end());
 }
 
 } // namespace castkeydrm