Windows: Drop support for Windows XP

XP is nearly 20 years old and there are hoops we jump through to keep
supporting it. Time to say goodbye and simplify some things.

Closes #267

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>
diff --git a/msvc/libusb_static_2015.vcxproj b/msvc/libusb_static_2015.vcxproj
index 336441b..ba07666 100644
--- a/msvc/libusb_static_2015.vcxproj
+++ b/msvc/libusb_static_2015.vcxproj
@@ -47,7 +47,7 @@
     <ClCompile>
       <AdditionalOptions>/utf-8 %(AdditionalOptions)</AdditionalOptions>
       <AdditionalIncludeDirectories>.;..\libusb;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
-      <PreprocessorDefinitions>WINVER=0x0501;_WIN32_WINNT=0x0501;_LIB;_CRT_SECURE_NO_WARNINGS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <PreprocessorDefinitions>_WIN32_WINNT=_WIN32_WINNT_VISTA;_LIB;_CRT_SECURE_NO_WARNINGS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
       <ProgramDataBaseFileName>$(IntDir)$(TargetName).pdb</ProgramDataBaseFileName>
       <WarningLevel>Level4</WarningLevel>
     </ClCompile>