Fixed warning CS0219 at EngineerTools.cs:50,20

The variable 'decimalMaskChar' is assigned but its value is never used

The warning was related to an improper variable name in duplicate code
within the number-to-string function SimpleFormatter method use to display
human-readable values. The variable in question triggers the printing of
digits after the decimal mark and could be modified to change the number
of digits to be shown. The two behaviours seem to have been separated
at one point and the trigger was deactivated. Comments have been added
in the relevant code section.
Minor: fixed warning CS1717 (x3) in Rendezvous.cs

Assignment made to same variable; did you mean to assign something else?

Variables named 'altitude' and 'bodyPosition' were double-assigned at
declaration. The slip was most likely introduced by automatic variable
renaming.
Minor: fixed warning CS0219 in Simulation.cs:559

The variable 'engineDecoupled' is assigned but its value is never used
Minor: fixed warning CS0414 in FlightEngineer.cs:76

Never used variable 'hasInstalledSDF'.
Fixed CS0414 in Rendezvous.cs:18

Never used variable 'scrollPosition'.

Seemingly, 'scrollPosition' was intended to refer to the eponymous
private parameter of FlightEngineer.settings and was locally defined
to avoid a compilation error. This fix makes the parameter public to
restore the intended behaviour.