Windows: Volatile: Remove explicit triple

`CMAKE_Swift_COMPILER_TARGET` is set up by `Build-CMakeProject`. We
shouldn't need to pass it into the volatile build explicitly.

Author: etcwilde

utils/build.ps1

@@ -2947,7 +2947,6 @@ function Build-ExperimentalRuntime([Hashtable] $Platform, [switch] $Static = $fa
       -Defines @{
         BUILD_SHARED_LIBS = if ($Static) { "NO" } else { "YES" };
         CMAKE_FIND_PACKAGE_PREFER_CONFIG = "YES";
-        CMAKE_Swift_COMPILER_TARGET = $Platform.Triple;
         CMAKE_STATIC_LIBRARY_PREFIX_Swift = "lib";
 
         SwiftCore_DIR = "${RuntimeBinaryCache}\cmake\SwiftCore";