STM: remove assertion not being true for nested, immediate, proofs (#4313)
STM: remove assertion not being true for nested, immediate, proofs (#4313)

gares/coq,barras/coq,coq/coq,jpdeplaix/coq,Matafou/coq,coq/coq,letouzey/coq-wip,silene/coq,TOSPIO/coq,8l/coq,gares/coq,ppedrot/coq,SkySkimmer/coq,coq/coq,JasonGross/coq,william-lawvere/coq,herbelin/github-coq,william-lawvere/coq,TheTypoMaster/coq,amintimany/coq,Ptival/coq,maximedenes/coq,ejgallego/coq,TheTypoMaster/coq,8l/coq,Zimmi48/coq,maximedenes/coq,TOSPIO/coq,barras/coq,maximedenes/coq,ppedrot/coq,gares/coq,amintimany/coq,Zimmi48/coq,silene/coq,Matafou/coq,SkySkimmer/coq,herbelin/github-coq,letouzey/coq-wip,JasonGross/coq,letouzey/coq-wip,coq/coq,Ptival/coq,barras/coq,Lionel-Rieg/coq,maximedenes/coq,ejgallego/coq,letouzey/coq-wip,amintimany/coq,ppedrot/coq,8l/coq,Zimmi48/coq,Matafou/coq,ppedrot/coq,silene/coq,william-lawvere/coq,maximedenes/coq,TheTypoMaster/coq,SkySkimmer/coq,ppedrot/coq,SkySkimmer/coq,Ptival/coq,mattam82/coq,Lionel-Rieg/coq,herbelin/github-coq,jpdeplaix/coq,JasonGross/coq,gares/coq,JasonGross/coq,TOSPIO/coq,mattam82/coq,letouzey/coq-wip,ejgallego/coq,mattam82/coq,jpdeplaix/coq,ejgallego/coq,Zimmi48/coq,gares/coq,Lionel-Rieg/coq