docs/templates/topindex.html: Replace usage of deprecated defindex.html.
docs/templates/topindex.html: Replace usage of deprecated defindex.html.

defindex.html (used by topindex.html) is deprecated, but topindex.html was
already identical other than setting the title, so just inherit directly
from layout.html.

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython