Make text object mappings silent

When using the `i,` and `a,` text objects you would see something like

    :call <SNR>24_VisualTextObject("\<SNR>24_OuterTextObject")

Or

    :call <SNR>24_VisualTextObject("\<SNR>24_InnerTextObject")

echoed on the command line. I added silent to the mappings to suppress that.