Delete disabled, failing spec tests introduces two errors

### HHVM Version

lab-3:/data2/swalk/play.021219a/hhvm$ hphp/hhvm/hhvm --version
HipHop VM 4.0.0-dev (rel)
Compiler: heads/master-0-gdde43d369a500e74bddae55ed19e5f94e4f4c3eb
Repo schema: 1bf2d68c8da00f38917959b5163415bb02bed849

### Operating System and Version

lab-3:/data2/swalk/play.021219a/hhvm$ uname -a
Linux lab-3 4.2.0 #1 SMP Wed Nov 25 14:00:54 CST 2015 aarch64 aarch64 aarch64 GNU/Linux

### Standalone code, or other way to reproduce the problem

hphp/test/run -v -m interp
hphp/test/run -v -m interp -r
hphp/test/run -v -m jit -a '-vEval.JitPGO=0'
hphp/test/run -v -m jit -r -a '-vEval.JitPGO=0'
hphp/test/run -v -m jit -a '-vEval.JitPGO=1'
hphp/test/run -v -m jit -r -a '-vEval.JitPGO=1'

### Actual result

Two tests consistently fail when repo option is used. Post-processed
report below. Columns line up with option sets above.

hphp/test/slow/spec/tests/expressions/postfix_operators/post-increment_and_decrement.php | . | F | . | F | . | F |
hphp/test/slow/spec/tests/expressions/unary_operators/pre-increment_and_decrement.php | . | F | . | F | . | F |

### Expected result

Pass

Show up in my testing of 02/12/2019. Bisected back to this commit
https://github.com/facebook/hhvm/commit/d827d5345de7a466cfa9e63e1e6e215c2154b9a3