[perl #47792] [BUG]: languages/dotnet/Configure.pl causes configuration error

[Will Coleda via RT]

r23011 added code to config/gen/languages.pm to configure dotnet when 
configuring parrot 
instead of (as before) manually, after parrot was built.

This isn't ready to happen yet. Reverting 23011 in spirit, dotnet is on its own 
again.

fixed in r23065.