remove tool: update-license-headers

This tool is not needed since license headers were removed in
d298719.

Author: andrewrk

test/standalone.zig

@@ -67,7 +67,6 @@ pub const simple_cases = [_]SimpleCase{
     .{ .src_path = "tools/gen_stubs.zig" },
     .{ .src_path = "tools/generate_linux_syscalls.zig" },
     .{ .src_path = "tools/process_headers.zig" },
-    .{ .src_path = "tools/update-license-headers.zig" },
     .{ .src_path = "tools/update-linux-headers.zig" },
     .{ .src_path = "tools/update_clang_options.zig" },
     .{ .src_path = "tools/update_cpu_features.zig" },