pgsql: Revert "Allow --with-bonjour to work with non-macOS implementati

Revert "Allow --with-bonjour to work with non-macOS implementations of Bonjour."

Upon further review, our Bonjour code doesn't actually work with the
Avahi not-too-compatible compatibility library. While you can get it
to work on non-macOS platforms if you link to Apple's own mDNSResponder
code, there don't seem to be many people who care about that. Leaving in
the AC_SEARCH_LIBS call seems more likely to encourage people to build
broken configurations than to do anything very useful.

Hence, remove the AC_SEARCH_LIBS call and put in a warning comment instead.

Discussion: https://postgr.es/m/[email protected]

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/28d177e3f95e3aef72f53e9e55096b350d1d5d9b

Modified Files
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configure | 58 ----------------------------------------------------------
configure.in | 8 ++++++--
2 files changed, 6 insertions(+), 60 deletions(-)