[fidl] Remove fidl_encode_{etc,msg}

These are only used by the C bindings.

Internal code search showed no other users.

This removes interesting tests; referencing the bug below so that this
commit can be found if/when someone wants to add those tests to GIDL.

Bug: 88460
Change-Id: I0abb889ebf041f03c3de4b486594813badb60c75
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/872196
API-Review: Adam Barth <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>
Reviewed-by: Yifei Teng <[email protected]>
Fuchsia-Auto-Submit: Tamir Duberstein <[email protected]>

Author: tamird

sdk/lib/fidl_base/BUILD.gn

@@ -53,7 +53,6 @@ sdk_source_set("fidl_base") {
 
   sources = [
     "decoding_and_validating.cc",
-    "encoding.cc",
     "formatting.cc",
     "handle_close_many.cc",
     "internal.c",