Revert "EXPERIMENTAL: let write update only the variant in the single-threaded case"
Revert "EXPERIMENTAL: let write update only the variant in the single-threaded case"

This reverts commit 57999d0418cd3f6119599b93c06a370e2da04ace.

jpfr/open62541,open62541/open62541,open62541/open62541,JGrothoff/open62541,jpfr/open62541,JGrothoff/open62541,jpfr/open62541,StalderT/open62541,AGIsmail/open62541,JGrothoff/open62541,AGIsmail/open62541,bostjanv/open62541,open62541/open62541,bostjanv/open62541,jpfr/open62541,JGrothoff/open62541,StalderT/open62541,StalderT/open62541,open62541/open62541,StalderT/open62541