fix: remove rpc_friendly.go (#2800)

Vendoring opentofu/tfdiags/rpc_friendly.go is not strictly needed but
caused issues with encoding/gob such as the one in the referenced issue.

Fixes #2784

pkg/vendored/generate.go

@@ -236,11 +236,6 @@ func vendorOpenTOFU(version string) {
 			dest:       "tfdiags/diagnostic_base.go",
 			transforms: transforms,
 		},
-		{
-			src:        "internal/tfdiags/rpc_friendly.go",
-			dest:       "tfdiags/rpc_friendly.go",
-			transforms: transforms,
-		},
 		{
 			src:        "internal/tfdiags/contextual.go",
 			dest:       "tfdiags/contextual.go",
@@ -271,9 +266,19 @@ func vendorOpenTOFU(version string) {
 			}),
 		},
 		{
-			src:        "internal/tfdiags/diagnostics.go",
-			dest:       "tfdiags/diagnostics.go",
-			transforms: transforms,
+			src:  "internal/tfdiags/diagnostics.go",
+			dest: "tfdiags/diagnostics.go",
+			transforms: append(transforms, func(s string) string {
+				code := `func (diags Diagnostics) ForRPC() Diagnostics {
+	ret := make(Diagnostics, len(diags))
+	for i := range diags {
+		ret[i] = makeRPCFriendlyDiag(diags[i])
+	}
+	return ret
+}
+`
+				return strings.ReplaceAll(s, code, "")
+			}),
 		},
 		{
 			src:        "internal/tfdiags/sourceless.go",

pkg/vendored/opentofu/tfdiags/diagnostics.go

@@ -123,13 +123,6 @@ func (diags Diagnostics) HasErrors() bool {
 // Note that this loses information about the original objects used to
 // construct the diagnostics, so e.g. the errwrap API will not work as
 // expected on an error-wrapped Diagnostics that came from ForRPC.
-func (diags Diagnostics) ForRPC() Diagnostics {
-	ret := make(Diagnostics, len(diags))
-	for i := range diags {
-		ret[i] = makeRPCFriendlyDiag(diags[i])
-	}
-	return ret
-}
 
 // Err flattens a diagnostics list into a single Go error, or to nil
 // if the diagnostics list does not include any error-level diagnostics.