MdeModulePkg: Remove NORETURN for PeiCore() and DxeMain() function

MdeModulePkg: Remove NORETURN for PeiCore() and DxeMain() function

PeiCore EntryPoint library _ModuleEntryPoint() will call PeiCore(), then call
CpuDeadLoop (). When NORETURN is added for PeiCore(), MSVC compiler will report
warning C4702: unreachable code for CpuDeadLoop (). And, the warning is treated
as error and cause build break. DxeMain() has the similar issue.

edk2 uses EntryPoint library to wrap every module entry point function except
for SEC. The module entry point is still called by _ModuleEntryPoint(). So,
there will be negative impact to add NORETURN for the module entry point.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Liming Gao <liming.gao@intel.com>