Remove license header from every file (#7689)

## What changed?
<!-- Describe what has changed in this PR -->
Remove license header from every file. Because it is really hard to
follow in this PR here is the summary:
1. License header is removed from all `.go` and `.proto` files
:fireworks::fireworks:🎆.
2. `LICENSE` file in the root directory has only Temporal and Uber
copyrights.
3. 5 other `LICENSE` files added to the packages which have copyrights
different from Temporal and Uber: Datadog, Xargin, "Mat Ryer, Tyler
Bunnell and contributors".
4. `license_file` flag is removed from all code generation tools.
5. `copyright_file` flag is removed from `go:generate mockgen`
directive.
6. All copyright related targets are removed from `Makefile`.
7. Updated Temporal copyright year to 2025 everywhere.

## Why?
<!-- Tell your future self why have you made these changes -->
I double checked with legal department that it is not needed to have
license header in every file. One file per repo is enough. I put all
copyrights to the root `LICENSE` file and removed header from all other
files. Also updated tools and `Makefile`.

develop/protoc.sh

@@ -26,7 +26,7 @@ color "Generate proto mocks..."
 find "$new" -name service.pb.go -o -name service_grpc.pb.go | while read -r src; do
   dst=$(echo "$src" | sed -e 's,service/,servicemock/,' -e 's,[.]go$,.mock.go,')
   pkg=$(basename "$(dirname "$(dirname "$dst")")")
-  $MOCKGEN -copyright_file LICENSE -package "$pkg" -source "$src" -destination "$dst"
+  $MOCKGEN -package "$pkg" -source "$src" -destination "$dst"
   # Since we're generating mocks from files in incorrect locations, mockgen
   # writes incorrect imports. Fix them manually. The awkward sed/rm invocation
   # is to work on linux and macos.
@@ -34,9 +34,6 @@ find "$new" -name service.pb.go -o -name service_grpc.pb.go | while read -r src;
   rm -f "$dst.replaced"
 done
 
-color "Update license headers for proto files..."
-go run ./cmd/tools/copyright/licensegen.go --scanDir "$new"
-
 color "Modify history service server interface..."
 sed -i.bak \
     -e 's/GetWorkflowExecutionHistory(context\.Context, \*GetWorkflowExecutionHistoryRequest) (\*GetWorkflowExecutionHistoryResponse, error)/GetWorkflowExecutionHistory(context.Context, *GetWorkflowExecutionHistoryRequest) (*GetWorkflowExecutionHistoryResponseWithRaw, error)/g' \