zink: do not require VK_KHR_external_memory

This is only required for the DRI-path. For the swrast code-path, we
don't need this.

We also don't need to explicitly test for it in the DRI-path, because we
test for KHR_external_memory_fd, which depends on KHR_external_memory. So
no implementation will expose the former without the latter.

Fixes: f1432fd3e2 ("zink: generate extension infrastructure using a python script")
Reviewed-by: Hoe Hao Cheng <haochengho12907@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7882>

src/gallium/drivers/zink/zink_device_info.py

@@ -58,7 +58,7 @@ import sys
 def EXTENSIONS():
     return [
         Extension("VK_KHR_maintenance1",             required=True),
-        Extension("VK_KHR_external_memory",          required=True),
+        Extension("VK_KHR_external_memory"),
         Extension("VK_KHR_external_memory_fd"),
         Extension("VK_KHR_vulkan_memory_model"),
         Extension("VK_EXT_conditional_rendering",    alias="cond_render", have_feature="conditionalRendering"),