Updated breakpoint import description, removed old "deprecated" import

[thexmanxyz]

@mahagr @RyanMPierson I noticed that under 04./10. there is a wrong description of the import procedure for using breakpoints within SCSS. Additionally there seems to be a leftover from the previous import procedure within the example code. Hence I rewrote the paragraph before the example SCSS to reflect what's really happening. We are not using @import "nucleus/mixins/breakpoints"; any more within the example so we should not describe the old routine here but rather describe what's happening when using @import "dependencies".

Additionally in the example code below (the last line) there was still the old import lurking around. Which probably was overseen during the docs update. So the description and the below example now clearly reflects what should be done when someone wants to use the breakpoint mixin without ambiguity.