pw_kvs: Always burn transaction IDs
pw_kvs: Always burn transaction IDs

This reverts a previous change to only bump transaction IDs on success,
and adds an explanation for why this is necessary.

Change-Id: I442d3f61b5d2a779e6b0681b91f09356f7c0eae9

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed