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

Run the six hphp/test/run commands listed in the report and inspect the two failing specs: hphp/test/slow/spec/tests/expressions/postfix_operators/post-increment_and_decrement.php and unary_operators/pre-increment_and_decrement.php. Review the bisected commit d827d5345de7a466cfa9e63e1e6e215c2154b9a3 and compare behavior with and without the repo option. Done means both tests pass in every listed mode.

Written by the indexing model from the issue text.