pgsql: Remove long-unused TransactionIdIsActive()

Remove long-unused TransactionIdIsActive()

TransactionIdIsActive() has not been used since bb38fb0d43c, in 2014. There
are no known uses in extensions either and it's hard to see valid uses for
it. Therefore remove TransactionIdIsActive().

Discussion: https://postgr.es/m/odgftbtwp5oq7cxjgf4kjkmyq7ypoftmqy7eqa7w3awnouzot6@hrwnl5tdqrgu

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f2c87ac04e73511a19dc36343f102eed3332573c

Modified Files
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src/backend/storage/ipc/procarray.c | 52 -------------------------------------
src/include/storage/procarray.h     |  1 -
2 files changed, 53 deletions(-)