Nuke TFIDFSim's cache [LUCENE-4577]

This is the old termscorer cache.

This helps nothing, and maybe hurts: I removed it and here are the results:
```
Chart saved to out.png... (wd: /home/rmuir/workspace/lucene-trunk/lucene/benchmark)
Task QPS base StdDev QPS patch StdDev Pct diff
TermGroup1M 52.87 (2.2%) 52.62 (2.4%) -0.5% ( -4% - 4%)
AndHighMed 34.82 (2.8%) 34.70 (3.6%) -0.3% ( -6% - 6%)
SpanNear 6.28 (5.3%) 6.26 (3.9%) -0.2% ( -8% - 9%)
IntNRQ 13.24 (11.0%) 13.24 (9.9%) 0.0% ( -18% - 23%)
Prefix3 42.19 (7.6%) 42.21 (7.0%) 0.1% ( -13% - 15%)
Wildcard 36.90 (6.8%) 37.02 (5.9%) 0.3% ( -11% - 13%)
AndHighHigh 25.68 (4.5%) 25.79 (3.2%) 0.5% ( -6% - 8%)
Phrase 9.28 (4.7%) 9.35 (4.4%) 0.7% ( -8% - 10%)
TermBGroup1M 45.76 (6.3%) 46.10 (3.2%) 0.7% ( -8% - 10%)
SloppyPhrase 10.25 (3.9%) 10.33 (4.4%) 0.8% ( -7% - 9%)
OrHighHigh 8.87 (6.4%) 8.97 (6.7%) 1.1% ( -11% - 15%)
Fuzzy1 70.28 (4.3%) 71.24 (7.1%) 1.4% ( -9% - 13%)
OrHighMed 10.70 (7.0%) 10.86 (6.4%) 1.5% ( -11% - 15%)
Fuzzy2 27.79 (6.1%) 28.31 (5.1%) 1.9% ( -8% - 13%)
Respell 71.72 (6.8%) 73.39 (3.7%) 2.3% ( -7% - 13%)
Term 209.49 (4.4%) 214.58 (3.7%) 2.4% ( -5% - 11%)
TermBGroup1M1P 7.10 (5.1%) 7.48 (7.8%) 5.3% ( -7% - 19%)
```

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Migrated from [LUCENE-4577](https://issues.apache.org/jira/browse/LUCENE-4577) by Robert Muir (@rmuir)
Attachments: [LUCENE-4577.patch](https://apache.github.io/lucene-jira-archive/attachments/LUCENE-4577/LUCENE-4577.patch)