Prior to this change, StandardServletEnvironment evaluated a
"jndiPropertySourceEnabled" flag to determine whether or not to add a
JndiPropertySource. Following the changes introduced in SPR-8490, there
is now no reason not to enable a JNDI property source by default. This
change eliminates the support for "jndiPropertySourceEnabled" and adds
a JndiPropertySource automatically.
Issue: SPR-8545, SPR-8490