OvmfPkg/EnrollDefaultKeys: remove unneeded EFIAPI call. conv. specifiers

OvmfPkg/EnrollDefaultKeys: remove unneeded EFIAPI call. conv. specifiers

The GetExact(), GetSettings(), PrintSettings() functions are only called
from within "EnrollDefaultKeys.c", and none of them take variable
arguments. Drop their EFIAPI calling convention specifiers.

Cc: Anthony Perard <anthony.perard@citrix.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Julien Grall <julien.grall@arm.com>
Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1747
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Gary Lin <glin@suse.com>