cvsserver: avoid warning about active db handles

cvsserver: avoid warning about active db handles

Turns out that DBD::SQLite does not favour preparing statements which are
never executed. So, turn all 4 statements, which were prepared _always_,
into methods, like the other 12 prepared statements.

Signed-off-by: Johannes Schindelin <redacted>
Signed-off-by: Junio C Hamano <redacted>