Clean up layout-files

• Change text to symbols
• Remove unused button-definitions.

This makes these layout-files easier to understand and edit.

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Checklist for checking that the layouts did not change

• am
• am+phonetic
• be
• be_wide
• bg
• bg+phonetic
• br
• ca
• cz
• cz+qwerty
• cz+qwerty_wide
• cz_wide
• de
• dk
• es
• es+cat
• fi
• fr
• fr+bepo
• fr+bepo_wide
• fr_wide
• ge
• gr
• gr+polytonic
• gr_wide
• il
• ir
• ir_wide
• no
• pl
• pl_wide
• ro
• ro_wide
• ru
• se
• se_wide
• th
• th_wide
• ua
• us
• us+colemak
• us+colemak_wide
• us+dvorak
• us+dvorak_wide
• us_wide
• email/us
• terminal/de
• terminal/de_wide
• terminal/us
• terminal/us+dvorak
• terminal/us+dvorak_wide
• terminal/us_wide
• url/us