chore: remove var declarations from DEPS that no longer have any effect (#45535)

* chore: Remove checkout_google_benchmark var that no longer has any effect

This variable stopped having any effect in https://chromium-review.googlesource.com/c/chromium/src/+/4322306

It was removed from Chromium entirely in https://chromium-review.googlesource.com/c/chromium/src/+/4339138

* chore: remove checkout_oculus_sdk and checkout_libaom from DEPS

DEPS

@@ -62,10 +62,6 @@ vars = {
 
   'checkout_nacl':
     False,
-  'checkout_libaom':
-    True,
-  'checkout_oculus_sdk':
-    False,
   'checkout_openxr':
     False,
   'build_with_chromium':
@@ -74,8 +70,6 @@ vars = {
     False,
   'checkout_android_native_support':
     False,
-  'checkout_google_benchmark':
-    False,
   'checkout_clang_tidy':
     True,
 }