theme: Remove some unsupported CSS properties

CSS opacity and border-{top,bottom}-{left,right}-radius are not
supported by St.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/957

data/theme/gnome-shell-sass/widgets/_calendar.scss

@@ -176,7 +176,6 @@
 
   .calendar-other-month-day {
     color: transparentize($fg_color ,0.5);
-    opacity: 0.5;
   }
 
   .calendar-week-number {

data/theme/gnome-shell-sass/widgets/_workspace-switcher.scss

@@ -46,9 +46,6 @@
 
   border-radius: $modal_radius 0 0 $modal_radius;
   border-right-width: 0 !important;
-  //fixme: can't have non uniform borders :(
-  border-top-left-radius:0 !important;
-  border-bottom-left-radius:0 !important;
 
   &:rtl { 
     border-radius: 0 $modal_radius $modal_radius 0;