gmt basemap -Bs -Bxaf draws full frame with WS axes annotated

`gmt basemap -Bs -Bxaf` draws full frame with WS axes annotated instead of just one X axis with ticks and no annotations and no other axes. I believe this is likely a bug. Same with `-Bx`, `-Bxa`.

I wanted to plot an X axis with ticks but no annotations for adding annotations externally for a complex plot.

I call `gmt basemap -R0/1/0/1 -JX5c -Bs -Bxaf -png test` and get a full frame with WS axes annotated and funny unproportionally long ticks:

after some testing I've got the needed result by running `gmt basemap -R0/1/0/1 -Jx5c -Bs -B -png test`