sbf_save_plot() should drop geometry column before saving xlsx

[StefanoMezzini]

Problem:

sbf_save_plot() fails to save the xlsx when the plot has a spatial layer because it can't save the geometry column in an xlsx file.

Steps to reproduce this behaviour:

library(sf)
library(ggplot2)
library(subfoldr2)

shp <- st_as_sf(data.frame(x = c(1, 2), y = c(10, 15)),
                coords = c("x", "y"))

ggplot(shp) + geom_sf()

sbf_save_plot(last_plot(), "plot", caption = "Caption.")
# Error:
# ! writexl cannot write column(s) of these types:
#   'geometry' (column 1): sfc_POINT/sfc (list)

Expected output/desired solution:

Drop the geometry column before saving the plot.