[SPARK-25089][R] removing lintr checks for 2.0

## What changes were proposed in this pull request?

since 2.0 will be EOLed some time in the not too distant future, and we'll be moving the builds from centos to ubuntu, i think it's fine to disable R linting rather than going down the rabbit hole of trying to fix this stuff.

## How was this patch tested?

the build system will test this

Closes #22074 from shaneknapp/removing-lintr-2.0.

Authored-by: shane knapp <incomplete@gmail.com>
Signed-off-by: Sean Owen <srowen@gmail.com>