Update flex to 2.6.1
* Flex has moved to Github, adjust download link
* Remove patch that has been applied upstream
* Disable building tests to avoid circular dependency to bison
  - disable also docs and examples at the same time

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>

SVN-Revision: 49025

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 39888