so_activex_x64: Avoid warning LNK4070

Don't specify optional library name in DEF file that is used both
for 32-bit and 64-bit library: it's explicitly specified in command
line.

Change-Id: I20e732f2095367ec3648741dde26cf7ec101f28f
Reviewed-on: https://gerrit.libreoffice.org/30008Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Mike Kaganski <mike.kaganski@collabora.com>

extensions/source/activex/so_activex.def

 ; iervp.def : Declares the module parameters.
 
-LIBRARY      "so_activex.dll"
+LIBRARY
 
 EXPORTS
 	DllCanUnloadNow     PRIVATE