remove unnecessary casting between XGL_CHAR/char

Many of the changed lines are generated.  That should be fixed at some point.
diff --git a/demos/tri.c b/demos/tri.c
index 0ca0d24..0059e03 100644
--- a/demos/tri.c
+++ b/demos/tri.c
@@ -812,9 +812,9 @@
     const XGL_APPLICATION_INFO app = {
         .sType = XGL_STRUCTURE_TYPE_APPLICATION_INFO,
         .pNext = NULL,
-        .pAppName = (const XGL_CHAR *) "tri",
+        .pAppName = "tri",
         .appVersion = 0,
-        .pEngineName = (const XGL_CHAR *) "tri",
+        .pEngineName = "tri",
         .engineVersion = 0,
         .apiVersion = XGL_MAKE_VERSION(0, 22, 0),
     };
@@ -828,7 +828,7 @@
         .queueCount = 1,
     };
     const XGL_CHAR *ext_names[] = {
-        (const XGL_CHAR *) "XGL_WSI_X11",
+        "XGL_WSI_X11",
     };
     const XGL_DEVICE_CREATE_INFO device = {
         .sType = XGL_STRUCTURE_TYPE_DEVICE_CREATE_INFO,