configure.ac: drop auto-detection of features

configure.ac: drop auto-detection of features

During the work with meson I realised auto-detection is not a good solution.
Our dependencies should be well-defined for what is considered 'normal' and
explicitly defined for any deviation from that normal build.

The normal build includes docs, tools, tests, etc. because we expect
developers to find errors in any of those. A distribution build may exclude
some of these bits, but it should be explicitly specified by the distribution
rather than having our build system guess what's not needed.

This patch drops any auto-detection of features and replaces it with a hard
yes/no.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>