There are a couple ways to paste text without the source formatting and one is to right click and select one of the alternative paste options. You can also accomplish this from the paste drop down menu of the Home tab on the Ribbon.
When pasting from Chrome, OneNote gives me the option to paste and:
- Keep Source Formatting
- Merge Formatting
- Paste only text
When you copy some other things (such as a chart from Excel) it gives you more pasting options to keep source data, paste as image, etc.
These are the paste icons shown below the paste button (in their respective order as described above) when you right click:
Here is the screen shot of the ribbon section:
Hope that helps