Decouple remote signer from client package internals.
Decouple remote signer from client package internals.

The remote signer previously relied on the (now internal) functions
for making raw requests. The remote signer now only relies on the
Remote interface specified in the client package.

j-delaney/cfssl,geligaoli/cfssl,jmhodges/cfssl,terinjokes/cfssl,codyli520/cfssl,mclem/cfssl,wl2002/cfssl,letsencrypt/cfssl,BugRoger/cfssl,dhiltgen/cfssl,terinjokes/cfssl,mclem/cfssl,codyli520/cfssl,sfurman3/cfssl,drcapulet/cfssl,j-delaney/cfssl,geligaoli/cfssl,mitchcapper/cfssl,j-delaney/cfssl,gtank/cfssl,thesamet/cfssl,mclem/cfssl,bifurcation/cfssl,bifurcation/cfssl,haneric21/cfssl,terinjokes/cfssl,APTy/cfssl,APTy/cfssl,jmhodges/cfssl,geligaoli/cfssl,rolandshoemaker/cfssl,rolandshoemaker/cfssl,endocode/cfssl,letsencrypt/cfssl,APTy/cfssl,BugRoger/cfssl,j-delaney/cfssl,BugRoger/cfssl,thesamet/cfssl,mclem/cfssl,haneric21/cfssl,haneric21/cfssl,drcapulet/cfssl,gtank/cfssl,mitchcapper/cfssl,codyli520/cfssl,gtank/cfssl,geligaoli/cfssl,endocode/cfssl,sdgdsffdsfff/cfssl,endocode/cfssl,drcapulet/cfssl,drcapulet/cfssl,bossjones/cfssl,sdgdsffdsfff/cfssl,gtank/cfssl,bifurcation/cfssl,bifurcation/cfssl,endocode/cfssl,BugRoger/cfssl,thesamet/cfssl,terinjokes/cfssl,bossjones/cfssl,geligaoli/cfssl,wl2002/cfssl,sfurman3/cfssl,haneric21/cfssl,jmhodges/cfssl,cloudflare/cfssl,sfurman3/cfssl,wl2002/cfssl,sdgdsffdsfff/cfssl,codyli520/cfssl,drcapulet/cfssl,bossjones/cfssl,bossjones/cfssl,dhiltgen/cfssl,dhiltgen/cfssl,rolandshoemaker/cfssl,rolandshoemaker/cfssl,codyli520/cfssl,endocode/cfssl,jmhodges/cfssl,mclem/cfssl,letsencrypt/cfssl,haneric21/cfssl,cloudflare/cfssl,dhiltgen/cfssl,j-delaney/cfssl,thesamet/cfssl,letsencrypt/cfssl,dhiltgen/cfssl,wl2002/cfssl,sfurman3/cfssl,mitchcapper/cfssl,cloudflare/cfssl,sfurman3/cfssl,wl2002/cfssl,APTy/cfssl,cloudflare/cfssl,APTy/cfssl,sdgdsffdsfff/cfssl,rolandshoemaker/cfssl