chore(makefile): remove residual add-license no-op target (#1788)

The license-check infrastructure (`check-license`, `install-addlicense`,
`install-hooks`, the bundled `addlicense` binary, and the git hooks
install) was already removed in commit 00ae644 (PR #1729). The
`add-license` target left behind only echoes a one-line message and
does nothing else, so it is dropped here along with its `.PHONY` entry.

License headers in source files are unchanged.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: earayu

Makefile

@@ -186,7 +186,7 @@ serve-web:
 ##################################################
 
 # Code quality checks
-.PHONY: format lint static-check add-license
+.PHONY: format lint static-check
 format:
 	uvx ruff check --fix ./aperag ./tests
 	uvx ruff format ./aperag ./tests
@@ -198,9 +198,6 @@ lint:
 static-check:
 	uvx mypy ./aperag
 
-add-license:
-	@echo "License headers are maintained in source files."
-
 # Testing suite
 .PHONY: test-all test-unit test-integration test-e2e test-e2e-perf \
 	test-http-bootstrap test-http-smoke test-http-full \