VS2015: Disable building DebugDLL opus_demo.

This works around the issue with using private symbols.

Signed-off-by: Ralph Giles <giles@mozilla.com>

win32/VS2015/opus.sln

 
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 14
-VisualStudioVersion = 14.0.25123.0
+VisualStudioVersion = 14.0.25420.1
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942}") = "opus", "opus.vcxproj", "{219EC965-228A-1824-174D-96449D05F88A}"
 EndProject
@@ -70,13 +70,9 @@ Global
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.Debug|x64.ActiveCfg = Debug|x64
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.Debug|x64.Build.0 = Debug|x64
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.DebugDLL_fixed|Win32.ActiveCfg = DebugDLL_fixed|Win32
-		{016C739D-6389-43BF-8D88-24B2BF6F620F}.DebugDLL_fixed|Win32.Build.0 = DebugDLL_fixed|Win32
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.DebugDLL_fixed|x64.ActiveCfg = DebugDLL_fixed|x64
-		{016C739D-6389-43BF-8D88-24B2BF6F620F}.DebugDLL_fixed|x64.Build.0 = DebugDLL_fixed|x64
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.DebugDLL|Win32.ActiveCfg = DebugDLL|Win32
-		{016C739D-6389-43BF-8D88-24B2BF6F620F}.DebugDLL|Win32.Build.0 = DebugDLL|Win32
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.DebugDLL|x64.ActiveCfg = DebugDLL|x64
-		{016C739D-6389-43BF-8D88-24B2BF6F620F}.DebugDLL|x64.Build.0 = DebugDLL|x64
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.Release|Win32.ActiveCfg = Release|Win32
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.Release|Win32.Build.0 = Release|Win32
 		{016C739D-6389-43BF-8D88-24B2BF6F620F}.Release|x64.ActiveCfg = Release|x64