BB 16285: Exclude ClearKey system for now

In the past the ClearKey system had not been compiled when specifying
--disable-eme. But that changed and it is even bundled nowadays (see:
Mozilla's bug 1300654). We don't want to ship it right now as the use
case for it is not really visible while the code had security
vulnerabilities in the past.

browser/installer/package-manifest.in

@@ -425,11 +425,11 @@ bin/libfreebl_64int_3.so
 #endif
 
 ; media
-@RESPATH@/gmp-clearkey/0.1/@DLL_PREFIX@clearkey@DLL_SUFFIX@
-@RESPATH@/gmp-clearkey/0.1/manifest.json
-#if defined(MOZ_WMF_CDM) && defined(ENABLE_TESTS)
-@BINPATH@/@DLL_PREFIX@wmfclearkey@DLL_SUFFIX@
-#endif
+;@RESPATH@/gmp-clearkey/0.1/@DLL_PREFIX@clearkey@DLL_SUFFIX@
+;@RESPATH@/gmp-clearkey/0.1/manifest.json
+;#if defined(MOZ_WMF_CDM) && defined(ENABLE_TESTS)
+;@BINPATH@/@DLL_PREFIX@wmfclearkey@DLL_SUFFIX@
+;#endif
 
 #ifdef MOZ_DMD
 ; DMD