Typography: Remove line-height placeholder

[hanneslsm]

Description

In the typography settings the placeholder that say "1.5" should be removed. It's confusing, especially if the default is not 1.5

Looks like there is already an existing issue #23895 but I'm proposing here simply to remove the placeholder as a quick fix to avoid confusion.

Step-by-step reproduction instructions

1. Create a theme and set in the theme.json the line height to anything you want, say 1.6
2. Go to the global styles and get confused why it says 1.5
3. This is also relevant for headings, and everywhere else where the typography setting exist

Screenshots, screen recording, code snippet

Environment info

• WP 6.2.2
• GB 16.0

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes