Track removal of String hash functions.

The number of virtual methods dropped by one. The change to the
field counting merits some explanation, with the change to OpenJDK
we got rid of two 16 bit fields and added a 32 bit field (which the
companion change removed), so things continued to work happily.
This change brings the number of 16 bit fields down to zero.

Also fixes 100-reflect2, which iterates over all methods in j.l.String.

bug: 28082128

(cherry picked from commit 5d8fa8bb)

Change-Id: I4e5454547e08b072768bbc466e2f5c027b8dab86