Improve type inference in Utilities

[odow]

Part of #1313

This was stopping the delete from precompiling:

After

Running: clp 
 18.562974 seconds (38.47 M allocations: 2.200 GiB, 5.93% gc time, 43.03% compilation time)
  0.001416 seconds (5.95 k allocations: 534.227 KiB)
Running: clp --no-bridge
 10.577259 seconds (18.82 M allocations: 1.070 GiB, 5.15% gc time, 96.09% compilation time)
  0.001221 seconds (3.01 k allocations: 309.070 KiB)
Running: glpk 
 14.450203 seconds (33.37 M allocations: 1.910 GiB, 6.87% gc time, 53.09% compilation time)
  0.000738 seconds (3.17 k allocations: 249.656 KiB)
Running: glpk --no-bridge
 11.603105 seconds (20.37 M allocations: 1.163 GiB, 5.11% gc time, 99.98% compilation time)
  0.000591 seconds (2.52 k allocations: 233.828 KiB)

[blegat]

Nice! You're getting good at this

[odow]

Not good enough to get the tests to pass... the 30 minute test time for MOI is a drag.