Use pyth sdk + tests

[0xripleys]

1. use PriceAccount and Product account from pyth-sdk-solana . removed some old code if there was a nicer way to do it with the sdk
2. use get_price_no_older_than (link). This lets us use the pyth price even if pyth hasn't updated in the last 2 minutes.
3. fix bpf tests
4. add tests for the get_pyth_price function
5. remove pyth.rs

partially addresses #111

[codecov-commenter]

Codecov Report

Merging #113 (83b5b9a) into upcoming (c602b70) will increase coverage by 0.51%.
The diff coverage is 93.87%.

@@             Coverage Diff              @@
##           upcoming     #113      +/-   ##
============================================
+ Coverage     78.83%   79.35%   +0.51%     
============================================
  Files            34       35       +1     
  Lines          9021     9115      +94     
============================================
+ Hits           7112     7233     +121     
+ Misses         1909     1882      -27     

Impacted Files	Coverage Δ
token-lending/program/tests/flash_borrow_repay.rs	88.72% <0.00%> (ø)
token-lending/program/src/state/obligation.rs	92.91% <50.00%> (ø)
token-lending/program/src/processor.rs	71.91% <71.42%> (+0.64%)	⬆️
token-lending/program/src/oracles.rs	96.55% <96.55%> (ø)
token-lending/program/src/state/lending_market.rs	97.05% <100.00%> (ø)
token-lending/program/src/state/reserve.rs	93.17% <100.00%> (ø)
...nding/program/tests/borrow_obligation_liquidity.rs	98.41% <100.00%> (+0.10%)	⬆️
token-lending/program/tests/helpers/mod.rs	88.93% <100.00%> (+0.08%)	⬆️
token-lending/program/tests/init_reserve.rs	100.00% <100.00%> (ø)
...ken-lending/program/tests/obligation_end_to_end.rs	99.38% <100.00%> (+<0.01%)	⬆️
... and 3 more

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