gdb/record-full: fix some -Wpessimizing-move errors

Compiling record-full.c with clang shows:

    /home/smarchi/src/binutils-gdb/gdb/record-full.c:2386:14: error: moving a temporary object prevents copy elision [-Werror,-Wpessimizing-move]
     2386 |         rec.entry = std::move (record_full_reg_entry::from_bfd
          |                     ^
    /home/smarchi/src/binutils-gdb/gdb/record-full.c:2386:14: note: remove std::move call here
     2386 |         rec.entry = std::move (record_full_reg_entry::from_bfd
          |                     ^~~~~~~~~~~
     2387 |                                 (cbfd, osec, bfd_offset));
          |                                                         ~
    /home/smarchi/src/binutils-gdb/gdb/record-full.c:2393:14: error: moving a temporary object prevents copy elision [-Werror,-Wpessimizing-move]
     2393 |         rec.entry = std::move (record_full_mem_entry::from_bfd
          |                     ^
    /home/smarchi/src/binutils-gdb/gdb/record-full.c:2393:14: note: remove std::move call here
     2393 |         rec.entry = std::move (record_full_mem_entry::from_bfd
          |                     ^~~~~~~~~~~
     2394 |                                 (cbfd, osec, bfd_offset));
          |                                                         ~

It's indeed not recommended to std::move the return value of a
function.  Remove the std::moves.

Change-Id: I80d947aa3d917fe3fcaaad0c3e329cb1de48a8ee