Remove unnecessary padding code

Bug: 213170822

Remove the code that CursorWindow::writeToParcel() uses to ensure slot
data is 4-byte aligned.  Because mAllocOffset and mSlotsOffset are
already 4-byte aligned, the alignment step here is unnecessary.

CursorWindow::spaceInUse() returns the total space used.  The tests
verify that the total space used is always a multiple of 4 bytes.

Test: atest
 * libandroidfw_tests

Change-Id: I720699093d5c5a584283e5b76851938f449ffa21