[Swift] Remove unused ATN.modeNameToStartState.
[Swift] Remove unused ATN.modeNameToStartState.

Remove unused ATN.modeNameToStartState.  In the Java runtime this is
only used by LexerATNFactory (i.e. during lexer generation) and we don't
have the equivalent in the Swift runtime at all.

ericvergnaud/antlr4,ericvergnaud/antlr4,antlr/antlr4,parrt/antlr4,ericvergnaud/antlr4,antlr/antlr4,ericvergnaud/antlr4,parrt/antlr4,antlr/antlr4,parrt/antlr4,ericvergnaud/antlr4,antlr/antlr4,ericvergnaud/antlr4,ericvergnaud/antlr4,antlr/antlr4,ericvergnaud/antlr4,antlr/antlr4,antlr/antlr4,parrt/antlr4,parrt/antlr4,parrt/antlr4,parrt/antlr4,antlr/antlr4,antlr/antlr4,parrt/antlr4,parrt/antlr4,ericvergnaud/antlr4,parrt/antlr4,ericvergnaud/antlr4,antlr/antlr4