kernel: Remove unused core_read.cpp from kernel

Also, util/string and util/strencodings

src/kernel/CMakeLists.txt

@@ -25,7 +25,6 @@ add_library(bitcoinkernel
   ../consensus/merkle.cpp
   ../consensus/tx_check.cpp
   ../consensus/tx_verify.cpp
-  ../core_read.cpp
   ../dbwrapper.cpp
   ../deploymentinfo.cpp
   ../deploymentstatus.cpp
@@ -72,8 +71,6 @@ add_library(bitcoinkernel
   ../util/rbf.cpp
   ../util/serfloat.cpp
   ../util/signalinterrupt.cpp
-  ../util/strencodings.cpp
-  ../util/string.cpp
   ../util/syserror.cpp
   ../util/threadnames.cpp
   ../util/time.cpp