depends: Purge libtool archives

We use pkg-config where we can, which generally replaces libtool at a
higher level and does not have the same downsides as libtool. These
archives sit in our depends tree with no purpose and pollute the final
bitcoin build with massive overlinking.

depends/packages/qrencode.mk

@@ -24,3 +24,7 @@ endef
 define $(package)_stage_cmds
   $(MAKE) DESTDIR=$($(package)_staging_dir) install
 endef
+
+define $(package)_postprocess_cmds
+  rm lib/*.la
+endef