libbinder: remove gMaxFds from Parcel

libbinder uses getrlimit to get the maximum number of file
descriptors and uses that limit to validate Flattenables.
This syscall is specific to Linux and Mac OS, so this patch
removes it and the gMaxFds variable. Parcel operations for
Flattenables with too many fds should fail anyway when
duplicating the descriptors using fcntl. This adds a test
to binderLibTest for that case.

Bug: 224644083
Test: atest binderLibTest
Change-Id: I7e969180c165c7ebed74c8a97098eb2265e0305c