doc: Clarify the getmempoolinfo.loaded RPC field documentation

Also, clarify the LoadMempool doxygen.

src/kernel/mempool_persist.cpp

@@ -19,7 +19,6 @@
 #include <util/time.h>
 #include <validation.h>
 
-#include <chrono>
 #include <cstdint>
 #include <cstdio>
 #include <exception>

src/kernel/mempool_persist.h

@@ -12,12 +12,12 @@ class CTxMemPool;
 
 namespace kernel {
 
-/** Dump the mempool to disk. */
+/** Dump the mempool to a file. */
 bool DumpMempool(const CTxMemPool& pool, const fs::path& dump_path,
                  fsbridge::FopenFn mockable_fopen_function = fsbridge::fopen,
                  bool skip_file_commit = false);
 
-/** Load the mempool from disk. */
+/** Import the file and attempt to add its contents to the mempool. */
 bool LoadMempool(CTxMemPool& pool, const fs::path& load_path,
                  Chainstate& active_chainstate,
                  fsbridge::FopenFn mockable_fopen_function = fsbridge::fopen);