build: delete 'configure.ac', bootstrap creates it from 'configure.ac.in'

'configure.ac' has to be with the context related information,
as 'fix number', 'release number', fields of MSDN version-info, ...

Using supplied (or not) options,
bootstrap will create the working 'configure.ac' as a modified version of 'configure.ac.in'.
build: define in configure.ac.in the common fields of version-info