Remove soong_docs from droidcore.

soong_docs will be run directly from soong_ui so it won't have a
corresponding Make target.

Test: Presubmits.
Change-Id: Id7abccdf2ea3830edf6043c10b617bddf4f9c86d
diff --git a/core/main.mk b/core/main.mk
index e1cfead..6b8080c 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -1670,8 +1670,7 @@
     $(INSTALLED_FILES_JSON_ROOT) \
     $(INSTALLED_FILES_FILE_RECOVERY) \
     $(INSTALLED_FILES_JSON_RECOVERY) \
-    $(INSTALLED_ANDROID_INFO_TXT_TARGET) \
-    soong_docs
+    $(INSTALLED_ANDROID_INFO_TXT_TARGET)
 
 # The droidcore target depends on the droidcore-unbundled subset and any other
 # targets for a non-unbundled (full source) full system build.