ae_source_module_exists in tools/ae.c is unused, which clang -Werror rejects #3486

ae_source_module_exists in tools/ae.c (added with 0d6029d) has no caller. ae_source_module_path is used directly instead. With clang, -Wall -Werror refuses the file (-Wunused-function), so building ae with clang under -Werror, or checking it with zig cc -Wall -Werror, needs -Wno-unused-function.

Expected: the function is removed, or used where ae_source_module_path is called only to test that the module exists.

Found while reviewing #3477; not part of it.