[lcm] Eschew LCM C++ API (use C instead)

[jwnimmer-tri]

Towards #17231.
See also #20115.

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This change is 

[jwnimmer-tri]

+@ggould-tri for feature review, please.

[ggould-tri]

Much simpler!

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: 2 unresolved discussions, needs at least two assigned reviewers

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-- commits line 2 at r1:
nit: Mention the alternative, since most people don't know LCM's full API buffet.

Suggestion:

- 2500a1e: [lcm] Eschew LCM C++ API (use C API instead)

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lcm/drake_lcm.cc line 10 at r1 (raw file):

#include <glib.h>
#include <lcm/lcm-cpp.hpp>

BTW: Took me a while to figure out why this was still here -- that styleguide prohibition on forward declaration really proves its point! :-)

[jwnimmer-tri]

+@sammy-tri for platform review per schedule, please.

Reviewable status: LGTM missing from assignee sammy-tri(platform)

[sammy-tri]

Reviewed 1 of 1 files at r2, all commit messages.
Reviewable status: LGTM missing from assignee sammy-tri(platform)

[sammy-tri]

Reviewable status: complete! all discussions resolved, LGTM from assignees ggould-tri(platform),sammy-tri(platform)

[RussTedrake]

After this commit, every bazel test I run in the manipulation repo that calls ApplyDefaultVisualization now fails with

connect: Network is unreachable

No route to 246.127.42.142

LCM requires a valid multicast route.  If this is a Linux computer and is
simply not connected to a network, the following commands are usually
sufficient as a temporary solution:

   sudo ifconfig lo multicast
   sudo route add -net 224.0.0.0 netmask 240.0.0.0 dev lo

For more information, visit:
   http://lcm-proj.github.io/lcm/multicast_setup.html

[jwnimmer-tri]

For reference, a probably-relevant detail here is that Russ's repositories block all kernel socket() calls by default:

https://github.com/RussTedrake/htmlbook/blob/bbc905e270eb4ca58bf059c812555b5a52d752b5/tools/python/defs.bzl#L19-L22

This was supposed to be a behavior-neutral change, so I'm reverting in #20136 until I understand why it changed.