APIv2: remove tx_history and ledger_header (#4759)

Remove `tx_history` and `ledger_header` methods from API version 2.

Update `RPC::Handler` to allow for methods (or method implementations)
to be API version specific. This partially resolves #4727. We can now
store multiple handlers with the same name, as long as they belong to
different (non-overlapping) API versions. This necessarily impacts the
handler lookup algorithm and its complexity; however, there is no
performance loss on x86_64 architecture, and only minimal performance
loss on arm64 (around 10ns). This design change gives us extra
flexibility evolving the API in the future, including other parts of
#4727.

In API version 2, `tx_history` and `ledger_header` are no longer
recognised; if they are called, `rippled` will return error
`unknownCmd`

Resolve #3638

Resolve #3539

src/test/basics/PerfLog_test.cpp

@@ -25,6 +25,7 @@
 #include <ripple/protocol/jss.h>
 #include <ripple/rpc/impl/Handler.h>
 #include <test/jtx/Env.h>
+#include <test/jtx/TestHelpers.h>
 
 #include <atomic>
 #include <chrono>
@@ -309,7 +310,8 @@ public:
 
         // Get the all the labels we can use for RPC interfaces without
         // causing an assert.
-        std::vector<char const*> labels{ripple::RPC::getHandlerNames()};
+        std::vector<char const*> labels =
+            test::jtx::make_vector(ripple::RPC::getHandlerNames());
         std::shuffle(labels.begin(), labels.end(), default_prng());
 
         // Get two IDs to associate with each label.  Errors tend to happen at