You could try Polycell aerosol stain block. This has worked for me in the past, A joiner had smeared silicon sealant in a very thin layer all over some doors, making it very difficult to remove. If the glazier has used it to bed-down the glass into the window frames, then you could try & cut-out the silicon with a stanley knife..just below the level of the window frame. Then fill the gap between the glass & the window frame with decorators caulk, & then level it off with a dampened filling knife.