Remove ./mach env as it is a lie.

We stopped overriding `$PATH` since using rustup.
The printed variables are not sufficient to do anything.

python/servo/bootstrap_commands.py

@@ -34,18 +34,6 @@
 
 @CommandProvider
 class MachCommands(CommandBase):
-    @Command('env',
-             description='Print environment setup commands',
-             category='bootstrap')
-    def env(self):
-        env = self.build_env()
-        print("export RUSTFLAGS=%s" % env.get("RUSTFLAGS", ""))
-        print("export PATH=%s" % env.get("PATH", ""))
-        if sys.platform == "darwin":
-            print("export DYLD_LIBRARY_PATH=%s" % env.get("DYLD_LIBRARY_PATH", ""))
-        else:
-            print("export LD_LIBRARY_PATH=%s" % env.get("LD_LIBRARY_PATH", ""))
-
     @Command('bootstrap',
              description='Install required packages for building.',
              category='bootstrap')