Remove runas and code no longer using it

tools/win/register_msdia80_dll.js

@@ -1,12 +0,0 @@
-var fs = require('fs')
-var path = require('path')
-var runas = require('runas')
-
-var source = path.resolve(__dirname, '..', '..', 'vendor', 'breakpad', 'msdia80.dll')
-var target = 'C:\\Program Files\\Common Files\\Microsoft Shared\\VC\\msdia80.dll'
-
-if (!fs.existsSync(target)) {
-  runas('cmd',
-    ['/K', 'copy', source, target, '&', 'regsvr32', '/s', target, '&', 'exit'],
-    {admin: true})
-}