[HWMemSimImpl] Remove "mem" from "ignore-read-enable-mem" flag

[fabianschuiki]

Remove the -mem suffix in the ignore-read-enable-mem option of the HWMemSimImpl pass. "Read enable" should be unambiguous already. Note that this does not change the corresponding firtool flag, so no breaking change of CLI flags happens here (except for direct circt-opt invocations).