remove COPY app instruction #294

Job	Run time
test_course_definition / docker_lint	7s
test_course_definition / go_lint	6s
test_course_definition / identify_language_slugs	3s
test_course_definition / markdown_lint	17s
test_course_definition / lint	53s
test_course_definition / js_lint	17s
test_course_definition / rust_lint	10s
test_course_definition / validate-schemas	24s
test_course_definition / validate-stages-naming	5s
test_course_definition / verify_templates_compiled	32s
test_course_definition / test (cpp)	1m 3s
test_course_definition / test (csharp)	47s
test_course_definition / test (gleam)	33s
test_course_definition / test (go)	46s
test_course_definition / test (haskell)	1m 49s
test_course_definition / test (javascript)	24s
test_course_definition / test (kotlin)	1m 40s
test_course_definition / test (python)	40s
test_course_definition / test (ruby)	27s
test_course_definition / test (rust)	44s
test_course_definition / test (typescript)	46s
	12m 33s

Provide feedback