Remnants of timestamp support still present

[marschall]

Even though timestamp support was removed in JAVAMONEY-89 it is still referenced in several places.

• class comment of ConversionContext
• class comment of CurrencyConversion
• class comment of CurrencyContext
• class comment of CurrencyQuery, fixed in Update CurrencyQuery to Make Timestamp Optional #117
• AbstractQuery#KEY_QUERY_TIMESTAMP, not referenced anywhere
• CurrencyConversionExceptionTest#CONTEXT100
• MonetaryRoundingsTest#testMonetaryRoundingsGetRoundingQueryWithLongTS()
• MonetaryRoundingsTest#testIsRoundingsAvailable_Query()

[keilw]

Seems removed by PRs like #119. What about the BP, do we care or leave it there? As it should go away with the next version, I am not sure, if it would break anything there, if not, then we may just keep it as it is.

[marschall]

#119 removes only one part, more remains to do
Removing AbstractQuery#KEY_QUERY_TIMESTAMP is a breaking change, I'm not sure we want to do this, maybe only deprecate.
As for the BP I'm not sure what the policy is. Most of these things are cosmetic only and do not affect functionality.