[AW] Remove unused //aw/apk:webview_license_provider_java

The last reference to this target was removed in crrev.com/i/2031130.

Test: autoninja -C out/aw system_webview_apk
Bug: 934152
Change-Id: I1c0fd238776e2346b77c83142a27b9d95a3854fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881493Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Commit-Queue: Robbie McElrath <rmcelrath@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710112}

android_webview/apk/BUILD.gn

@@ -12,10 +12,6 @@ generate_jni("apk_jni_headers") {
   ]
 }
 
-# Empty target to avoid breaking Clank.
-java_group("webview_license_provider_java") {
-}
-
 # Contains classes needed by the webview apk, but not used when loading the apk
 # as a library.
 android_library("apk_java") {