[cleanup] Remove -no_intercept_all_signals

Dropping support for -no_intercept_all_signals and removing the option would simplify some of the signal-handling code. I do not think we'll ever go back to not intercepting all signals. Xref #2311 where we may want to reduce emulation for the signal mask, but I don't think we'd want to or be able to reduce emulation of signal handling/delivery.