Update unique field creates multiple indexes

[lrkwz]

Bug Report

Steps to Reproduce

1. Create a collection named test
2. Add a unique field named code
3. execute in mysql SHOW CREATE TABLE test on the collection you created, there is a single UNIQUE KEY index on the field
4. Update any attribute of the field
5. repeat SHOW CREATE TABLE test on the updated collection, now there are two UNIQUE KEY indexes

Expected Behavior

A single UNIQUE KEY index per unique field

Actual Behavior

As many UNIQUE KEY indexes as many updates you execute

Technical Details

• Device: desktop
• OS: ubuntu 18.04
• Web Server: docker image 2.0.5
• PHP Version: docker image 2.0.5
• Database: docker image 2.0.5
• Install Method: docker image 2.0.5