Actually, the data look like it has scientific notation, so you don't want to remove the E. In R scientific notation is represented with a small e. In other words, 9.9e2 or 9.9e-2.
A simple solution for your data is to multiply by 1:
> 9.9000000000000005E-2*1
[1] 0.099
# or
df2 <- df %>% mutate(obesity = obesity*1)
Although, I would confirm with the person who put the data together if this was explicit, or if it was just the way that R read the data. Understanding your data is the most important thing before starting any analysis.