Rename unzip.cpp to ziptool.cpp.

It contains unzip and zipinfo, and will likely contain zip too soon.

Test: builds
Change-Id: I017df302108847f29bfdd120f20bf0fd3b9caa5b
diff --git a/libziparchive/Android.bp b/libziparchive/Android.bp
index a20ae03..1bbffaf 100644
--- a/libziparchive/Android.bp
+++ b/libziparchive/Android.bp
@@ -177,7 +177,7 @@
 cc_binary {
     name: "ziptool",
     defaults: ["libziparchive_flags"],
-    srcs: ["unzip.cpp"],
+    srcs: ["ziptool.cpp"],
     shared_libs: [
         "libbase",
         "libziparchive",
diff --git a/libziparchive/unzip.cpp b/libziparchive/ziptool.cpp
similarity index 100%
rename from libziparchive/unzip.cpp
rename to libziparchive/ziptool.cpp