Bug 1494844 Remove an unused MOZ_PLUGIN_CONTAINER define r=jld

In Bug 1114647 we added this define, and it was used in ipc/contentproc/plugin-container.cpp
However its use there was removed as part of MOZ_PLUGIN_CONTAINER

Differential Revision: https://phabricator.services.mozilla.com/D7155

--HG--
extra : moz-landing-system : lando

Author: tomrittervg

ipc/app/moz.build

@@ -78,7 +78,5 @@ if CONFIG['OS_ARCH'] == 'WINNT' and CONFIG['CC_TYPE'] not in ('clang', 'gcc'):
 if CONFIG['CC_TYPE'] in ('clang', 'gcc'):
     CXXFLAGS += ['-Wshadow']
 
-DEFINES['MOZ_PLUGIN_CONTAINER'] = 1;
-
 with Files("**"):
     BUG_COMPONENT = ("Core", "DOM: Content Processes")