Remove $type-scale SCSS variables

Remove $type-scale SCSS variables from _variables.scss and replace usage with appropriate GitLab UI design token or variable.

Remove class generators from utilities.scss

@each $index, $size in $type-scale {
  #{'.text-#{$index}'} {
    font-size: $size;
  }
}

@each $index, $size in $type-scale {
  #{'.lh-#{$index}'} {
    line-height: $size;
  }
}

lh- classes don't appear to be used. There's some usage of .text-1, .text-2, .text-3, .text-4, .text-5, classes which could be replaced with like values from Tailwind generated gl-text-size classes