val: Remove source from validation result

This was just echoing back the source that was provided to the
validation routine, and is no longer uses by any callers.

Change-Id: I55aeb7c41405ebbe1b21b9654b94607b651ff118
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/57281
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>

src/val/hlsl.cc

@@ -41,8 +41,6 @@ Result HlslUsingDXC(const std::string& dxc_path,
     return result;
   }
 
-  result.source = source;
-
   utils::TmpFile file;
   file << source;
 
@@ -113,8 +111,6 @@ Result HlslUsingFXC(const std::string& source,
     return result;
   }
 
-  result.source = source;
-
   for (auto ep : entry_points) {
     const char* profile = "";
     switch (ep.second) {

src/val/msl.cc

@@ -32,10 +32,8 @@ Result Msl(const std::string& xcrun_path, const std::string& source) {
     return result;
   }
 
-  result.source = source;
-
   utils::TmpFile file(".metal");
-  file << result.source;
+  file << source;
 
 #ifdef _WIN32
   // On Windows, we should actually be running metal.exe from the Metal

src/val/val.h

@@ -37,8 +37,6 @@ struct Result {
   bool failed = false;
   /// Output of DXC.
   std::string output;
-  /// The generated source that was compiled
-  std::string source;
 };
 
 /// Hlsl attempts to compile the shader with DXC, verifying that the shader