Remove constant propagation from static-switch test.

Constant propagation might be going away, but static-switches are likely
here to stay. Avoid conflating the two in this test.

Change-Id: If4b6c99c85f124d3bbc20da858693f09f5e4fd59
Bug: skia:11319
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/374117
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

resources/sksl/errors/StaticSwitchTest.sksl

@@ -1,6 +1,5 @@
 half4 main() {
-    int x = int(sqrt(1));
-    @switch (x) {
+    @switch (int(sqrt(1))) {
         case 1:
             return half4(1);
         default:

tests/sksl/errors/StaticSwitchTest.glsl

@@ -1,4 +1,4 @@
 ### Compilation failed:
 
-error: 3: static switch has non-static test
+error: 2: static switch has non-static test
 1 error