Remove get-task-allow entitlement from signed builds

This entitlement allows debugger to hook in to the app and allow other
apps to call `task_for_pid()` on MacVim, and Apple has discouraged its
use. In fact, the only reason why MacVim passes app notarization is
because it has also set the disable-library-validation entitlement
which allows get-task-allow to be set. We don't actually need
get-task-allow in release binary builds as we don't intentionally want
to allow external debuggers and code injection, so we should just remove
it.

This was previously added in #980 where we made a mistake in assuming
that get-task-allow was what was needed to sign the app with hardened
runtime while allowing scripting interface (e.g. Python) to work, but
that was wrong. It was the disable-library-validation entitlment
instead, as we need the ability to load in unsigned libraries as
Python distributions from say Homebrew are not signed.

Credit: This was pointed out by Karol Mazurek

Author: ychin

src/MacVim/MacVim.entitlements

@@ -6,7 +6,5 @@
     <true/>
     <key>com.apple.security.cs.disable-library-validation</key>
     <true/>
-    <key>com.apple.security.get-task-allow</key>
-    <true/>
 </dict>
 </plist>