Revert "Minor doc improvement"

This reverts commit d58b613.

Actually, 1.0+ values should be fine since the value is relative to the
total amount of available RAM.

Author: michaelklishin

docs/rabbitmq.config.example

@@ -260,7 +260,6 @@
    %% Alternatively, we can set a limit relative to total available RAM.
    %%
    %% Values lower than 1.0 can be dangerous and should be used carefully.
-   %% As a rule of thumb, values between 1.5 and 2.0 fit most cases.
    %% {disk_free_limit, {mem_relative, 2.0}},
 
    %%