[FAB-6341] Is mkdocs.yml necessary?
[FAB-6341] Is mkdocs.yml necessary?

This CR deletes mkdocs.yml. This file was used by Github.
But now fabric uses sphinx for making documents.

Change-Id: I8980b169c55cf04af1e253f0dd3d72f4335d4dfc
Signed-off-by: Nao Nishijima <ba12c351dbe96870a968dc0b0668a4a809432a94@hal.hitachi.com>

manish-sethi/fabric-sidedb,ckeyer/fabric,muralisrini/fabric,hyperledger/fabric,stemlending/fabric,lukehuangch/fabric,xixuejia/fabric,ckeyer/fabric,jimthematrix/fabric,manish-sethi/fabric,binhn/fabric,manish-sethi/fabric,manish-sethi/fabric-sidedb,xixuejia/fabric,ckeyer/fabric,lukehuangch/fabric,lukehuangch/fabric,stemlending/fabric,ckeyer/fabric,ckeyer/fabric,stemlending/fabric,lukehuangch/fabric,manish-sethi/fabric-sidedb,muralisrini/fabric,jimthematrix/fabric,xixuejia/fabric,lukehuangch/fabric,ckeyer/fabric,manish-sethi/fabric-sidedb,stemlending/fabric,lukehuangch/fabric,manish-sethi/fabric-sidedb,hyperledger/fabric,muralisrini/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,binhn/fabric,ckeyer/fabric,lukehuangch/fabric,binhn/fabric