mesa: remove api_loopback to remove call indirections

This is an optimization for SPECviewperf.

The increase in lines of code is only 14%.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6874>

src/mesa/main/context.c

@@ -80,7 +80,6 @@
 
 #include "accum.h"
 #include "api_exec.h"
-#include "api_loopback.h"
 #include "arrayobj.h"
 #include "attrib.h"
 #include "bbox.h"
@@ -1084,7 +1083,7 @@ _mesa_alloc_dispatch_table(void)
  *      OPERATION."
  *
  * The table entries for specifying vertex attributes are set up by
- * install_vtxfmt() and _mesa_loopback_init_api_table(), and End() and dlists
+ * install_vtxfmt(), and End() and dlists
  * are set by install_vtxfmt() as well.
  */
 static struct _glapi_table *
@@ -1130,8 +1129,6 @@ create_beginend_table(const struct gl_context *ctx)
    COPY_DISPATCH(ObjectPurgeableAPPLE);
    COPY_DISPATCH(ObjectUnpurgeableAPPLE);
 
-   _mesa_loopback_init_api_table(ctx, table);
-
    return table;
 }