refactor(docs-infra): remove unused styles from `_sidenav.scss` (#40704)
refactor(docs-infra): remove unused styles from `_sidenav.scss` (#40704)

This commit removes some styles from `_sidenav.scss` that are no longer
used (i.e. either their CSS selectors do not match any element in the
app or they are overridden by other rules).

PR Close #40704

gkalpak/angular,brandonroberts/angular,ocombe/angular,angular/angular,alxhub/angular,angular-indonesia/angular,mgechev/angular,alxhub/angular,angular/angular,gkalpak/angular,gnomeontherun/angular,alxhub/angular,brandonroberts/angular,brandonroberts/angular,angular/angular,manekinekko/angular,manekinekko/angular,ocombe/angular,angular-indonesia/angular,manekinekko/angular,JiaLiPassion/angular,shairez/angular,shairez/angular,JiaLiPassion/angular,mgechev/angular,brandonroberts/angular,mgechev/angular,shairez/angular,mgechev/angular,gnomeontherun/angular,alxhub/angular,manekinekko/angular,ocombe/angular,manekinekko/angular,gkalpak/angular,gnomeontherun/angular,JiaLiPassion/angular,gnomeontherun/angular,gkalpak/angular,angular-indonesia/angular,brandonroberts/angular,shairez/angular,angular/angular,ocombe/angular,angular-indonesia/angular,JiaLiPassion/angular,manekinekko/angular,ocombe/angular,ocombe/angular,brandonroberts/angular,alxhub/angular,mgechev/angular,shairez/angular