On Win32, i_rpcsvcdbm should be 'undef' as there is no <rpcsvc/dbm.h>

3 canned Win32 config files had i_rpcsvcdbm as 'define', and consequently
their generated headers had I_RPCSVC_DBM defined. This symbol means that
a header file <rpcsvc/dbm.h> exists and should be included. However, it's
only used by ODBM_File, which is not built on Win32, so nothing ever noticed
the error.

The errors in the header files seem to date from commit 0a753a764065f226
("[inseparable changes from patch from perl5.003_23 to perl5.003_24]" in
Jan 1997), which added the Win32 port. The config file, win32/config.w32,
has i_rpcsvcdbm as 'undef' but the header file win32/config.h is
inconsistent, with I_RPCSVC_DBM defined.

The errors in the canned configs seem to date from commit 68dc074516a6859e
("[inseparable changes from match from perl-5.003_93 to perl-5.003_94]" in
March 1997), where the value of i_rpcsvcdbm was changed in win32/config.w32