build: prune compat event headers

The *_compat headers are the deprecated / non-threadsafe versions of the
current headers. There's no need for us to ship them in depends. Prune
them are save the safe / nuke the possibility of them being used.

depends/packages/libevent.mk

@@ -37,5 +37,6 @@ endef
 
 define $(package)_postprocess_cmds
   rm lib/*.la && \
-  rm include/ev*.h
+  rm include/ev*.h && \
+  rm include/event2/*_compat.h
 endef