Revert "added -verafxmul compiler option to use vera fx multiplication routine on cx16"

This reverts commit 690782bf.
It was too risky, using vera (especially fx) transparently in multiple places especially perhaps in IRQ handlers will create havoc unless much intricate care is taken to save/restore the vera state. Better to do vera fx explicitly where the programmer has full control.

codeCore/src/prog8/code/core/CompilationOptions.kt

@@ -21,7 +21,6 @@ class CompilationOptions(val output: OutputType,
                          var experimentalCodegen: Boolean = false,
                          var varsHighBank: Int? = null,
                          var splitWordArrays: Boolean = false,
-                         var veraFxMul: Boolean = false,
                          var outputDir: Path = Path(""),
                          var symbolDefs: Map<String, String> = emptyMap()
 ) {