How to trim a string by finding multiple words
Replacing multiple substrings is fairly easy to do with REPLACE commands inside of a CASE block.
I successfully tested the following command on MySQL 5.6:
select
    case
        when my_string like '% (RES)%' then replace(my_string, ' (RES)', '')
        when my_string like '% (R)%' then replace(my_string, ' (R)', '')
        else my_string
    end as my_string_without_characters
from
    sample_table;

Shameless plug: I tested this command across multiple databases and posted about it on my blog here: How to replace multiple substrings with SQL.