Dissolvant for the black spots around the rear mirror of the front window of my car
The part of the windshield that you are talking about is called the frit. This is typically made up of some form of high-heat enamel, and as far as I was able to find, it is intended to increase the surface roughness of the inside of the glass to increase the ability for the adhesive to stick to it. 

I was not able to find any specific mention for what type of enamel frits are actually made of - that is whether it is an enamel glass or an enamel paint -  and as such I cannot give any specific recommendations for what solvent to use. If it is enamel glass, as I would hazard to guess it is - given that some sources indicate that it is applied prior to the windshield being bent - then you will likely not be able to remove the frit without also damaging the glass. If it is an enamel paint then you may be able to remove it with an organic solvent. In general, I like to start with acetone as a general organic solvent. 

All of this said, given both the purpose of the frit, and its proximity to the adhesive that holds your windshield on, I strongly recommend that you consider moving your dashcam rather than attempting to dissolve the frit.  

Best of luck.