title: Can't remove gridlines when plotting with geom_sf
body: <p>The standard means of removing gridlines seem futile when plotting with <code>geom_sf</code>. </p>
  
  <p>For instance, if we plot a simple <code>ggplot</code> object, this works to remove the grid </p>
  
  <pre><code>library(tidyverse)
  library(sf)
  
  mtcars %&gt;%
    ggplot(
      aes(disp, hp)
    ) +
    geom_point() +
    theme(
      panel.grid.major = element_blank(),
      panel.grid.minor = element_blank()
    )
  </code></pre>
  
  <p>returns</p>
  
  <p><a href="https://i.stack.imgur.com/IdMe9.png" rel="noreferrer"><img src="https://i.stack.imgur.com/IdMe9.png" alt="scatterplot no grid"></a></p>
  
  <p>but the same code fails to remove the grid when you plot using <code>geom_sf</code></p>
  
  <pre><code>"shape/nc.shp" %&gt;% 
    system.file(
      package = "sf"
    ) %&gt;% 
    st_read(
      quiet = TRUE
      ) %&gt;%
    ggplot() +
    geom_sf(aes(fill = AREA)) +
    theme(
      panel.grid.major = element_blank(),
      panel.grid.minor = element_blank()
    )
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/k34Z2.png" rel="noreferrer"><img src="https://i.stack.imgur.com/k34Z2.png" alt="enter image description here"></a></p>