AAPT2: Increase maximum proto size

Deserializing a proto form a string throws an error when 64MB have been
read from the stream. This change removes the maximum size but shows a
warning when a proto is larger than 64MB.

Bug: 114020398
Test: manual test with resources.pb greater than 64MB
Change-Id: Iee397b6709d79a9338133a6136fe6e8f70a4964c