CachedAppOptimizer: Remove use of hardcoded PAGE_SIZE 4096

bionic hard codes the PAGE_SIZE macro as 4096. This is going away as
Android begins to support larger page sizes. Remove the usage of this
assumption from CachedAppOptimizer source; use instead getpagesize()
which provides the real pagesize.

Test: mma
Bug: 295082310
Change-Id: I2adc60ffa38bd23442a08cbd80b68f0158057c5e
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>