Bug 40414: Update stable.entitlements.xml

Update stable.entitlements.xml with the version currently in use on the
signing machine.

tools/signing/stable.entitlements.xml

@@ -20,9 +20,6 @@
     <!-- Code paged in from disk should match the signature at page in-time -->
     <key>com.apple.security.cs.disable-executable-page-protection</key><false/>
 
-    <!-- Allow loading third party libraries. Needed for Flash and CDMs -->
-    <key>com.apple.security.cs.disable-library-validation</key><true/>
-
     <!-- Allow dyld environment variables. Needed because Firefox uses
          dyld variables to load libaries from within the .app bundle. -->
     <key>com.apple.security.cs.allow-dyld-environment-variables</key><true/>