editorconfig: remove redundant parts

[pjonsson]

What this PR does

The indentation size for everything
has been 2 since commit a8c927d
in 2019, so remove the extra section
for scss files that specify the same
value.

Test me

Open an scss file in an editor that respects .editorconfig and see that the indentation size is still 2.

Checklist

• There are unit tests to verify my changes are correct or unit tests aren't applicable (if so, write quick reason why unit tests don't exist)
• I've updated relevant documentation in doc/.
• I've updated CHANGES.md with what I changed.
• I've provided instructions in the PR description on how to test this PR.