RFR: JDK-8141414 Deprecate configure source overriding

[Magnus Ihse Bursie]

In the initial build-infra setup, it was possible to selectively replace 
individual repos (e.g. corba). This has never been widely used, and has 
not been tested or supported for a long time. It recently turned out to 
be broken on hotspot.

We should deprecate this functionality.
Bug: https://bugs.openjdk.java.net/browse/JDK-8141414
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8141414-deprecate-source-overriding/webrev.01

/Magnus