BaseTools/tools_def.template: eliminate GCC44_IA32_X64_DLINK_FLAGS

BaseTools/tools_def.template: eliminate GCC44_IA32_X64_DLINK_FLAGS

GCC48_IA32_X64_DLINK_FLAGS is defined *wholly* as
GCC44_IA32_X64_DLINK_FLAGS, therefore:

- expand the contents of GCC44_IA32_X64_DLINK_FLAGS into
  GCC48_IA32_X64_DLINK_FLAGS,

- re-point all references of GCC44_IA32_X64_DLINK_FLAGS to
  GCC48_IA32_X64_DLINK_FLAGS,

- remove GCC44_IA32_X64_DLINK_FLAGS.

Cc: Bob Feng <bob.c.feng@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1377
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>