Removes references to bundled libuv.

--- a/src/Makevars	2020-07-31 11:53:30.576484531 +0200
+++ b/src/Makevars	2020-07-31 11:54:19.369863118 +0200
@@ -5,7 +5,7 @@
 
 UNAME := $(shell uname)
 
-PKG_LIBS = ./libuv/.libs/libuv.a ./http-parser/http_parser.o ./sha1/sha1.o ./base64/base64.o -pthread
+PKG_LIBS = -luv ./http-parser/http_parser.o ./sha1/sha1.o ./base64/base64.o -pthread
 
 ifeq ($(UNAME), Darwin)
 PKG_LIBS += -framework CoreServices
@@ -23,7 +23,7 @@
 
 PKG_CFLAGS = $(C_VISIBILITY) -DSTRICT_R_HEADERS
 PKG_CXXFLAGS = $(CXX_VISIBILITY) -DSTRICT_R_HEADERS
-PKG_CPPFLAGS = -Ilibuv/include -pthread
+PKG_CPPFLAGS = -pthread
 
 # To avoid spurious warnings from `R CMD check --as-cran`, about compiler
 # warning flags like -Werror.
@@ -43,35 +43,5 @@
 # PKG_CPPFLAGS += -D_GLIBCXX_ASSERTIONS
 
 
-$(SHLIB): libuv/.libs/libuv.a http-parser/http_parser.o sha1/sha1.o base64/base64.o
+$(SHLIB): http-parser/http_parser.o sha1/sha1.o base64/base64.o
 
-# We needed to rename lt~obsolete.m4 because the name causes problems with R
-# CMD check. Here we rename it back.
-libuv/m4/lt~obsolete.m4: libuv/m4/lt_obsolete.m4
-	cp -p -f libuv/m4/lt_obsolete.m4 libuv/m4/lt~obsolete.m4
-
-# Run ./configure. We need to touch various autotools-related files to avoid
-# it trying to run autotools programs again. We also need to make sure
-# configure is executable, because on some platforms, calling unzip() in R
-# does not preserve the executable bit.
-#
-# It's VERY IMPORTANT that mtime(aclocal.m4) <= mtime(configure), and also
-# mtime(aclocal.m4) <= mtime(Makefile.in). On some platforms, passing multiple
-# files to a single touch command gives them all the same time, but on others
-# (Solaris and possibly some Fedoras) the timestamps are slightly increasing
-# from one to the next, i.e. the order matters. To remove this fragility, we
-# use "-r aclocal.m4" to ensure that all three files are guaranteed to have
-# precisely the same timestamp value.
-libuv/Makefile: libuv/m4/lt~obsolete.m4
-	(cd libuv \
-		&& touch aclocal.m4 \
-		&& touch -r aclocal.m4 configure Makefile.in \
-		&& chmod +x configure \
-		&& CC="$(CC)" CFLAGS="$(CFLAGS) $(CPICFLAGS) $(C_VISIBILITY)" AR="$(AR)" RANLIB="$(RANLIB)" LDFLAGS="$(LDFLAGS)" ./configure $(CONFIGURE_FLAGS))
-
-libuv/.libs/libuv.a: libuv/Makefile
-	$(MAKE) --directory=libuv \
-		HAVE_DTRACE=0
-
-clean:
-	$(MAKE) --directory=libuv distclean