Remove short real-specific executables from build

[ceblanton]

Currently, these short real-specific executables are built: PLEV.r4.exe and TAVG.r4.exe. Both of these are run through wrapper scripts, plevel.sh and timavg.csh respectively. plevel.sh does not have an option to use PLEV.r4.exe so it can be summarily removed.

timavg.csh has an option to use the r4 executable but defaults to the r8 (full real) version. FRE (frepp) does not use the r4 option though, so it can be safely removed (the timavg.csh precision option and the r4 executable).

• Remove PLEV.r4.exe from build
• RemoveTAVG.r4.exe from build
• Remove --precision option from timavg.csh

@underwoo suggested this change to facilitate the automake build process.