delete rustfmt.toml using nightly options

rustfmt.toml

@@ -1,16 +0,0 @@
-format_strings = true
-format_macro_matchers = true
-imports_layout = "HorizontalVertical"
-merge_imports = true
-match_block_trailing_comma = true
-merge_derives = true
-newline_style = "Unix"
-normalize_comments = true
-reorder_impl_items = true
-space_after_colon = true
-space_before_colon = false
-struct_lit_single_line = false
-type_punctuation_density = "Wide"
-use_field_init_shorthand = true
-use_try_shorthand = true
-wrap_comments = true