Do not override configure recipe and do not invoke upstream autogen.sh.
The shipped autogen.sh attempts to call "gtkdocize" which is no guaranteed
build prereq of LEDE or OpenWrt.

Also add a patch to disable the processing of documentation, tests and
examples as these resources rely on gtk-doc infrastructure which is not
available within LEDE or OpenWrt.

Example error for the bad autogen.sh invocation:

    ( cd .../loudmouth-1.5.3; ./autogen.sh )
    ./autogen.sh: 33: ./autogen.sh: gtkdocize: not found
    Makefile:73: recipe for target '.../.configured_yynyyyyn' failed

Example error for the lacking gtk-doc automake infrastructure:

    automake: error: cannot open < gtk-doc.make: No such file or directory
    autoreconf: .../host/bin/automake failed with exit status: 1
    [...]
    config.status: error: cannot find input file: `docs/reference/Makefile.in'
    Makefile:72: recipe for target '.../.configured_yynyn' failed

Signed-off-by: Jo-Philipp Wich <jo@mein.io>