Bug 1420092 - Don't always enable mozjemalloc by default when building the js engine. r=njn

The target.kernel-based tests should be enough.

--HG--
extra : rebase_source : 6dce05a8c097af1402dc98a3fa75a2ef581ef862

build/moz.configure/memory.configure

@@ -14,14 +14,11 @@ option('--enable-jemalloc', env='MOZ_MEMORY',
        help='Replace memory allocator with jemalloc')
 
 
-@depends('--enable-jemalloc', target, build_project, c_compiler)
-def jemalloc(value, target, build_project, c_compiler):
+@depends('--enable-jemalloc', target, c_compiler)
+def jemalloc(value, target, c_compiler):
     if value.origin != 'default':
         return bool(value) or None
 
-    if build_project == 'js':
-        return True
-
     if target.kernel in ('Darwin', 'Linux'):
         return True