Add doc for Request.Builder.removeHeader. (#3858)
Add doc for Request.Builder.removeHeader. (#3858)

to note multiple headers may be removed.
tiarebalbi/okhttp,jrodbx/okhttp,cmzy/okhttp,square/okhttp,tiarebalbi/okhttp,cketti/okhttp,yschimke/okhttp,ansman/okhttp,ansman/okhttp,ansman/okhttp,cketti/okhttp,yschimke/okhttp,ze-pequeno/okhttp,square/okhttp,yschimke/okhttp,jrodbx/okhttp,cketti/okhttp,ze-pequeno/okhttp,ze-pequeno/okhttp,square/okhttp,cmzy/okhttp,tiarebalbi/okhttp,jrodbx/okhttp