remove unused octicons
remove unused octicons

these are now in `@nteract/octicons`

nteract/nteract,nteract/nteract,nteract/nteract,jdfreder/nteract,jdfreder/nteract,nteract/composition,nteract/nteract,jdfreder/nteract,nteract/nteract,jdfreder/nteract,rgbkrk/nteract,rgbkrk/nteract,rgbkrk/nteract,rgbkrk/nteract,nteract/composition,rgbkrk/nteract,nteract/composition