Strip zip64 extras after writing local header when copying

writeHeader generates zip64 extras that are correct for the local
header, but incorrect for the central directory header.  Strip the
extras again after writeHeader so that the central directory header
extras are recreated correctly.

Test: Zip2Zip64
Bug: 296314205
Change-Id: I1ca6a5745a9f97426df6c111db444facdfa25b2e