pgsql: Remove dynahash.h

Remove dynahash.h

All the callers of my_log2() are now limited inside dynahash.c, so let's
remove this header.  The same capability is provided by pg_bitutils.h
already.

Discussion: https://postgr.es/m/CAEZATCUJPQD_7sC-wErak2CQGNa6bj2hY-mr8wsBki=kX7f2_A@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/e6da68a6e1d60a037b63a9c9ed36e5ef0a996769

Modified Files
--------------
src/backend/utils/hash/dynahash.c |  4 ++--
src/include/utils/dynahash.h      | 20 --------------------
2 files changed, 2 insertions(+), 22 deletions(-)