triagebot: disable auto stable-regression compiler backport nominations

No prejudice against re-enabling them if the nominations include a bit
more context on _why_ it's automatically nominated and _which_
regression(s) are being addressed. Or as proposed, it could also simply
become a reminder-to-nominate _comment_.

Author: jieyouxu

triagebot.toml

@@ -61,10 +61,6 @@ required-issue-label = "regression-from-stable-to-beta"
 # if the above conditions matches, the PR will receive these labels
 add-labels = ["beta-nominated"]
 
-[backport.t-compiler-stable-backport]
-required-pr-labels = ["T-compiler"]
-required-issue-label = "regression-from-stable-to-stable"
-add-labels = ["stable-nominated"]
 
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