EmbeddedPkg/TimeBaseLib: remove the SEC_PER_MONTH, SEC_PER_YEAR macros

The SEC_PER_MONTH and SEC_PER_YEAR macros are wrong: they both evaluate to
0 (of type "int"). They are also unused (they could never be used for
division, for example); so remove them. The macros were originally
introduced in commit 0f4386e7 ("ArmPlatformPkg/PL031RealTimeClockLib:
Implement PL031 RTC drive", 2011-06-11).

Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Reported-by: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20200904154541.23340-1-lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>