Revert "watchOS target os"

This reverts commit 7ae1d75869.

Reason for revert: breaks flutter build

Original change's description:
> watchOS target os
>
> - add support for --os=watchos | --os=watchos_simulator
> - do not depend on perfetto if dart_support_perfetto is false
> - change the default value for dart_support_perfetto to !is_watchos
>
> To minimize changes and to avoid modifying third-party zlib BUILD file, is_watchos implies is_ios for now.
>
> TEST=manual, no watchOS SDK on bots yet.
>
> Cq-Include-Trybots: luci.dart.try:vm-mac-debug-arm64-try,vm-mac-release-arm64-try
> Change-Id: If2130068ef546162a07a9ba53f94b11ff25fb565
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/415021
> Reviewed-by: Ryan Macnak <rmacnak@google.com>
> Commit-Queue: Ivan Inozemtsev <iinozemtsev@google.com>

Cq-Include-Trybots: luci.dart.try:vm-mac-debug-arm64-try,vm-mac-release-arm64-try
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I4bede9ede04ac3c533b8ff7ae2f1adbd84eb2397
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/425262
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>
Auto-Submit: Ivan Inozemtsev <iinozemtsev@google.com>

utils/aot_snapshot.gni

@@ -174,7 +174,7 @@ template("aot_snapshot") {
     output_prefix = "lib"
     output_extension = ""
 
-    if (current_os == "mac" || current_os == "ios" || current_os == "watchos") {
+    if (current_os == "mac" || current_os == "ios") {
       output_extension = "dylib"
     } else if (current_os == "win") {
       output_extension = "dll"