Drop useenv=true also from the 32-bit build script: It is not necessary and

leads to failures in successive 64-bit/32-bit builds in the same shell window.

Tools/buildbot/build.bat

@@ -2,7 +2,7 @@
 cmd /c Tools\buildbot\external.bat
 call "%VS100COMNTOOLS%vsvars32.bat"
 cmd /c Tools\buildbot\clean.bat
-msbuild /p:useenv=true PCbuild\kill_python.vcxproj /p:Configuration=Debug /p:PlatformTarget=x86
+msbuild PCbuild\kill_python.vcxproj /p:Configuration=Debug /p:PlatformTarget=x86
 PCbuild\kill_python_d.exe
-msbuild /p:useenv=true PCbuild\pcbuild.sln /p:Configuration=Debug /p:Platform=Win32
+msbuild PCbuild\pcbuild.sln /p:Configuration=Debug /p:Platform=Win32