[Impeller] Remove unused flag enable-impeller-vulkan.

ci/builders/linux_host_engine.json

@@ -39,7 +39,6 @@
               "debug",
               "--unoptimized",
               "--prebuilt-dart-sdk",
-              "--enable-impeller-vulkan",
               "--target-dir",
               "host_debug_impeller_vulkan"
           ],

impeller/docs/renderdoc_frame_capture.md

@@ -9,7 +9,7 @@
 # In your $ENGINE_SRC folder, do:
 
 ./flutter/tools/gn --unopt --no-lto --enable-impeller-playground\
-   --enable-impeller-vulkan --target-dir host_debug_impeller_vulkan
+   --target-dir host_debug_impeller_vulkan
 autoninja -C out/host_debug_impeller_vulkan/
 ```
 

tools/gn

@@ -964,6 +964,7 @@ def parse_args(args):
       action='store_true',
       help='Whether impeller unit tests run in playground mode.'
   )
+
   parser.add_argument(
       '--prebuilt-impellerc',
       default=None,
@@ -972,15 +973,6 @@ def parse_args(args):
       'Do not use this outside of CI or with impellerc from a different engine version.'
   )
 
-  # This is currently a no-op, will be removed shortly.
-  parser.add_argument(
-      '--enable-impeller-vulkan',
-      default=False,
-      action='store_true',
-      help='Enables WIP impeller support for vulkan. ' +
-      'https://github.com/flutter/flutter/issues/107357'
-  )
-
   parser.add_argument(
       '--enable-impeller-3d',
       default=False,