RFR (XS) 8232734 [TESTBUG] avoid using JDK symbols in ExtraSymbols.symbols.txt

[Ioi Lam]

https://bugs.openjdk.java.net/browse/JDK-8232734
http://cr.openjdk.java.net/~iklam/jdk14/8232734-avoid-jdk-symbols-in-extra-symbols-test.v01/

ExtraSymbols.symbols.txt contains symbols that were once
extracted from the JDK. This has caused confusion when
developers are removing APIs from the JDK, and they are not
sure if they should also remove the corresponding symbols in
this file.

In this patch, ExtraSymbols.symbols.txt is removed altogether. Instead,
a text file is generated at run time to cover the necessary cases.

Tested with hs-tier1/2.

Thanks
- Ioi