Revert following changes for fixing Primetime issue:

- Issue #26 Part 2a: make more EME code conditional. (99118e38e)
- Issue #26 - Part 2b: Stub out GMPDecryptorProxy functions. (d44c61bf6)
- Issue #26 - Part 2c: Remove dependence on gmp/widevine-adapter/* (4c9689f68)
- Issue #1392 - Change --enable-eme to MOZ_ARG_ENABLE_BOOL and remove MOZ_EME_MODULES (832d84d2c)
- [Basilisk] Issue MoonchildProductions/UXP#1392 - Remove usage of MOZ_EME_MODULES (3a165cd)
- Issue #65 - Remove AppConstants from toolkit/mozapps/extensions (758618b60)

dom/media/gmp/GMPDecryptorProxy.h

@@ -6,9 +6,7 @@
 #ifndef GMPDecryptorProxy_h_
 #define GMPDecryptorProxy_h_
 
-#ifdef MOZ_EME
 #include "mozilla/DecryptorProxyCallback.h"
-#endif
 #include "GMPCallbackBase.h"
 #include "gmp-decryption.h"
 #include "nsString.h"
@@ -17,13 +15,8 @@ namespace mozilla {
 class CryptoSample;
 } // namespace mozilla
 
-#ifdef MOZ_EME
 class GMPDecryptorProxyCallback : public DecryptorProxyCallback,
                                   public GMPCallbackBase {
-#else
-class GMPDecryptorProxyCallback : public GMPCallbackBase {
-#endif
-
 public:
   virtual ~GMPDecryptorProxyCallback() {}
 };