Removed signing config in app/build.gradle
Removed signing config in app/build.gradle

Change-Id: I5e7c05ce0733a24817a5ae8091f507c766ab777e

KazumiHARADA/TvCleanArchitecture2,AdamRLukaitis/androidtv-Leanback,Karmacons/DragonTV,seventhmoon/androidtv-Leanback,cartland/androidtv-Leanback,leasual/androidtv-Leanback,thiagoricieri/androidtv-Leanback,mstarvid/androidtv-Leanback,SeanPONeil/HyprMX-AndroidTV-Leanback,littleli/androidtv-Leanback,tmack8001/androidtv-Leanback,libinbensin/androidtv-Leanback,ramialcheikh/leanback,googlearchive/androidtv-Leanback,yhirano/androidtv-Leanback,googlesamples/androidtv-Leanback,juoni/androidtv-Leanback,marcbaechinger/androidtv-Leanback,netconstructor/androidtv-Leanback