Avoid displaying duplicative "Type / to choose a block" prompts

[kean]

What problem does this address?

What is your proposed solution?

• Remove the "Type / to choose a block" prompt, as it's a rarely used feature on mobile (tracks needed)
• Add a one-time tip to teach the user about the "/"
• Consider showing tips only when you connect a hardware keyboard
• (Alternative) show "Type / to choose a block" only for the very first empty paragraph block in an empty post

[dcalhoun]

Noting the duplicate prompts no longer occur in the current beta release, it was likely addressed by upgrading Gutenberg packages.

I'll leave this issue open for us to consider further improvements.