tests, base: Removed dead code from base/intmath

tests, base: Removed dead code from base/intmath

The below list of functions were dead code and are now
deleted.
intmath.prevPrime, intmath.isPrime, intmath.leastSigBit,
intmath.floorPow2, intmath.ceilPow2, intmath.isHex,
intmath.isOct, intmath.isDec, intmath.hex2Int. The source
file intmath.cc is now effectively useless and deleted.

Change-Id: I28e4350056b8d03e02fecd5c7f7f9c62bc2df7ce
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/22584
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Gabe Black <gabeblack@google.com>