Do not include default column limit in schema.rb

Follow up of #20815.

```ruby
class CreatePeople < ActiveRecord::Migration[5.0]
  def change
    create_table :people do |t|
      t.integer :int
      t.bigint :bint
      t.text :txt
      t.binary :bin
    end
  end
end
```

Result.

In postgresql and sqlite3 adapters:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt"
    t.binary  "bin"
  end

end
```

In mysql2 adapter:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4" do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt",  limit: 65535
    t.binary  "bin",  limit: 65535
  end

end
```

After this patch:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4" do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt"
    t.binary  "bin"
  end

end
```

1 files changed, 1 insertions, 1 deletions

diff --git a/activerecord/test/cases/adapters/mysql2/charset_collation_test.rb b/activerecord/test/cases/adapters/mysql2/charset_collation_test.rb
index 668c07dacb..c8028b6b36 100644
--- a/activerecord/test/cases/adapters/mysql2/charset_collation_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/charset_collation_test.rb
@@ -49,6 +49,6 @@ class Mysql2CharsetCollationTest < ActiveRecord::Mysql2TestCase
   test "schema dump includes collation" do
     output = dump_table_schema("charset_collations")
     assert_match %r{t.string\s+"string_ascii_bin",\s+collation: "ascii_bin"$}, output
-    assert_match %r{t.text\s+"text_ucs2_unicode_ci",\s+limit: 65535,\s+collation: "ucs2_unicode_ci"$}, output
+    assert_match %r{t.text\s+"text_ucs2_unicode_ci",\s+collation: "ucs2_unicode_ci"$}, output
   end
 end