Revert "make sure write_timeout and local_infile ivars are setup to avoid warnings.

This reverts commit e7e43411c5fd3191605b0dfb4d0dfb97c1466561.

I added initializing for ```read_timeout``` because it is used [here](https://github.com/brianmario/mysql2/blob/41f8b327a4029c9dce507eda24d5401891ac5cec/ext/mysql2/client.c#L466). There was case, when that instance variable wasn't initialized and it caused warning, because it was read uninitialized from C Ruby API via ```rb_iv_get```.

I think we don't need to initialize another variables. I was looking for another instance variables, but I found only ```query_options``` (already initialized) and ```current_query_options``` which is already initialized in C extension. There is no case where ```write_timeout``` or ```local_infile``` is set into instance variable. There are just writers to set it into mysql via C extension for ```write_timeout``` and ```local_infile```.