Remove mcoverlayfs code

mcoverlayfs code is now unused (technically should work on top of the
soft emulation but not well tested, and untested unused code is bad).
Remove it.

Left the unshare/bind_mount_recursive code in mcexec in a new
MCEXEC_BIND_MOUNT ifdef (only in config.h.in directly to discourage use.
it disables the ioctl as well, but the main code is still compiled to
keep up to date with linux api changes... although it's using kallsyms
lookup so it does not validate much more than "the symbol still exists")

I honestly think this should go as well (people who would want to use it
are root and could do it manually), but will give up for now.

Change-Id: I832b6a8ab19e24ed67a1a5044b1c6c32381ae0aa

CMakeLists.txt

@@ -78,7 +78,6 @@ set_property(CACHE BUILD_TARGET PROPERTY STRINGS smp-x86 smp-arm64)
 set(ENABLE_MEMDUMP ON)
 option(ENABLE_PERF "Enable perf support" ON)
 option(ENABLE_RUSAGE "Enable rusage support" ON)
-option(ENABLE_MCOVERLAYFS "Enable overlay filesystem" OFF)
 option(ENABLE_QLMPI "Enable qlmpi programs" OFF)
 option(ENABLE_UTI "Enable uti support" OFF)
 option(ENABLE_UBSAN "Enable undefined behaviour sanitizer on mckernel size" OFF)
@@ -142,9 +141,6 @@ configure_file(config.h.in config.h)
 
 # actual build section - just subdirs
 add_subdirectory(executer/kernel/mcctrl)
-if (ENABLE_MCOVERLAYFS)
-	add_subdirectory(executer/kernel/mcoverlayfs)
-endif()
 add_subdirectory(executer/user)
 add_subdirectory(kernel)
 add_subdirectory(tools/mcstat)
@@ -188,7 +184,6 @@ message("KBUILD_C_FLAGS: ${KBUILD_C_FLAGS}")
 message("ENABLE_MEMDUMP: ${ENABLE_MEMDUMP}")
 message("ENABLE_PERF: ${ENABLE_PERF}")
 message("ENABLE_RUSAGE: ${ENABLE_RUSAGE}")
-message("ENABLE_MCOVERLAYFS: ${ENABLE_MCOVERLAYFS}")
 message("ENABLE_QLMPI: ${ENABLE_QLMPI}")
 message("ENABLE_UTI: ${ENABLE_UTI}")
 message("ENABLE_WERROR: ${ENABLE_WERROR}")