Convert .PHONY target of `checkapi ` to Android.bp

Since Soong has been able to correctly add dependencies to .PHONY
targets since aosp/2884366, it is now possible to directly use
`phony_deps` to add the genrules used by `checkapi` to its dependencies
and convert them to Android.bp.

Bug: 309730110
Test: m checkapi
Change-Id: Ideb9f647415423a5864d221b85442b995ac67906

api/Android.bp

@@ -458,3 +458,12 @@ genrule {
         targets: ["droid"],
     },
 }
+
+phony_rule {
+    name: "checkapi",
+    phony_deps: [
+        "frameworks-base-api-current-compat",
+        "frameworks-base-api-system-current-compat",
+        "frameworks-base-api-module-lib-current-compat",
+    ],
+}

api/Android.mk

-.PHONY: checkapi
-checkapi: frameworks-base-api-current-compat frameworks-base-api-system-current-compat frameworks-base-api-module-lib-current-compat