Moved nghttp2 to epan
Cleaned up nghttp2 build

Change-Id: I9f7adc12936155e0ffc01ec825b5aff95279f97d
Reviewed-on: https://code.wireshark.org/review/2937
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Evan Huus <eapache@gmail.com>