Confusing #if nesting in hmac_openssl.c

I noticed that buildfarm member batfish has been complaining like
this for awhile:

hmac_openssl.c:90:1: warning: unused function 'ResourceOwnerRememberHMAC' [-Wunused-function]
hmac_openssl.c:95:1: warning: unused function 'ResourceOwnerForgetHMAC' [-Wunused-function]

Looking at the code, this is all from commit e6bdfd970, and apparently
batfish is our only animal that doesn't HAVE_HMAC_CTX_NEW.  I tried to
understand the #if nesting and soon got very confused.  I don't think
it is helpful to put the resource owner manipulations inside #ifdef
HAVE_HMAC_CTX_NEW and HAVE_HMAC_CTX_FREE --- probably, it would never
be the case that only one of those is defined, but it just seems
messy.  What do you think of rearranging it as attached?

			regards, tom lane