Remove a couple unnecessary type aliases

al/source.cpp

@@ -988,7 +988,7 @@ bool SetSourcefv(ALsource *Source, ALCcontext *Context, SourceProp prop, const a
         if(IsPlayingOrPaused(Source))
         {
             ALCdevice *device{Context->mDevice.get()};
-            BackendLockGuard _{*device->Backend};
+            std::lock_guard<BackendBase> _{*device->Backend};
             /* Double-check that the source is still playing while we have the
              * lock.
              */
@@ -1215,7 +1215,7 @@ bool SetSourceiv(ALsource *Source, ALCcontext *Context, SourceProp prop, const a
 
         if(IsPlayingOrPaused(Source))
         {
-            BackendLockGuard _{*device->Backend};
+            std::lock_guard<BackendBase> _{*device->Backend};
             if(ALvoice *voice{GetSourceVoice(Source, Context)})
             {
                 auto vpos = GetSampleOffset(Source);

alc/alc.cpp

@@ -4240,7 +4240,7 @@ START_API_FUNC
         alcSetError(dev.get(), ALC_INVALID_VALUE);
     else
     {
-        BackendLockGuard _{*dev->Backend};
+        std::lock_guard<BackendBase> _{*dev->Backend};
         aluMixData(dev.get(), buffer, static_cast<ALuint>(samples), dev->channelsFromFmt());
     }
 }

alc/backends/base.h

@@ -54,8 +54,6 @@ struct BackendBase {
     virtual ~BackendBase();
 };
 using BackendPtr = std::unique_ptr<BackendBase>;
-using BackendUniqueLock = std::unique_lock<BackendBase>;
-using BackendLockGuard = std::lock_guard<BackendBase>;
 
 enum class BackendType {
     Playback,