pdl: remove “checksum start precedes checksum field” lint

This lint is wrong, it is okay for the checksum start to start before
the checksum field itself. We have real files in the wild that uses
this construct, such as l2cap_packets.pdl.

Bug: 238865051
Test: atest pdl_inline_tests
Change-Id: I5d709a0fefdbdede704f799b46a20f523459d604