Simplify ziputils

zip_sections was taking a reader by value and then returning it.

But we don't have to do that - for both Read and Seek, if X satisfies
the trait then so does &mut X. So if the caller wants to retain their
reader, they can just pass us a mutable reference to it.

Bug: 299591171
Test: atest libapkverify.test libapkverify.integration_test
Change-Id: Ic849d3c15843a712c8014c342569a42e7becf4b8
diff --git a/libs/apkverify/src/sigutil.rs b/libs/apkverify/src/sigutil.rs
index 395b493..99132b6 100644
--- a/libs/apkverify/src/sigutil.rs
+++ b/libs/apkverify/src/sigutil.rs
@@ -51,8 +51,8 @@
 }
 
 impl<R: Read + Seek> ApkSections<R> {
-    pub fn new(reader: R) -> Result<ApkSections<R>> {
-        let (mut reader, zip_sections) = zip_sections(reader)?;
+    pub fn new(mut reader: R) -> Result<ApkSections<R>> {
+        let zip_sections = zip_sections(&mut reader)?;
         let (signing_block_offset, signing_block_size) =
             find_signing_block(&mut reader, zip_sections.central_directory_offset)?;
         Ok(ApkSections {