Remove conditionals in ambuild scripts for using msvc <2013 (not supported).

AMBuildScript

@@ -216,8 +216,6 @@ class SMConfig(object):
         '_CRT_NONSTDC_NO_DEPRECATE',
         '_ITERATOR_DEBUG_LEVEL=0',
       ]
-      if cxx.version < 1800:
-        cxx.defines += 'strtoull=_strtoui64'
       cxx.cflags += [
         '/W3',
       ]

core/AMBuilder

@@ -78,10 +78,6 @@ for sdk_name in SM.sdks:
       vs_year = ''
       if msvc_ver == 1800:
         vs_year = '2013'
-      elif msvc_ver == 1700:
-        vs_year = '2012'
-      elif msvc_ver == 1600:
-        vs_year = '2010'
       else:
         raise Exception('Cannot find libprotobuf for MSVC version "' + compiler.version + '"')