Remove rxode2et

[mattfidler]

• [x] Error (test-alag.R:25:3): (code run outside oftest_that())
• [x] Error (test-backward.R:172:7): Add sampling makes sense
• [x] Error (test-backward.R:182:7): Add dosing makes sense
• [x] Error (test-cbind-study-individual.R:48:3): cbind study and individual
• [x] Error (test-meanProb.R:49:5): test meanProb()
• [x] Error (test-plot.R:104:5): plot() with invalid component throws an error
• [x] Error (test-rxode-issue-375.R:45:5): mixing omega and sigma with parameter data frame; RxODE#375
• [x] Error (test-zzzz-plot.R:145:7): plot tests

[mattfidler]

• [x] There are ::: calls to the package's namespace in its code: ‘.rxSEeq’
• [x] _rxode2_calcDerived
• [x] _rxode2_getWh
• [x] _rxode2_linCmtParse
• [x] _rxode2_linCmtParse
• [x] _rxode2_parseFreeSexp
• [x] _rxode2_linCmtParse
• [x] _rxode2_getClassicEvid
• [x] _rxode2_getRxFn
• [x] _rxode2_rxQr
• [x] _rxode2_rxQs
• [x] _rxode2_rxode2parseSetRstudio