protocols: remove unused fieldpath option

The +fieldpath option, specific to gogoprotobuf, enabled dynamic field
access in protobuf messages, allowing nested fields to be accessed via
string paths.

This change is part of a larger effort to transition to the official Go
protobuf library for better maintainability and community support.
Upon review, no instances of dynamic field access were found in the
codebase, confirming that the feature is not in use.

By removing this unused feature, we simplify the build process and make
it easier to complete the transition away from gogoprotobuf.

Signed-off-by: Beraldo Leal <bleal@redhat.com>

src/libs/protocols/hack/update-generated-proto.sh

@@ -55,7 +55,7 @@ generate_go_sources() {
 
     local root_path=$(realpath ../)/libs/protocols/protos
     local cmd="protoc -I$GOPATH/src:${root_path} \
---gogottrpc_out=plugins=ttrpc+fieldpath,paths=source_relative,\
+--gogottrpc_out=plugins=ttrpc,paths=source_relative,\
 Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types\
 :$(realpath ../)/runtime/virtcontainers/pkg/agent/protocols/$dir_path \
 ${root_path}/$file_name"