gccrs: Remove Parser::parse_tuple_index_expr_float

gccrs: Remove Parser::parse_tuple_index_expr_float

Unlike in C, floating point literals can't start with a '.', and
therefore could never be split into a '.' followed by an integer.

gcc/rust/ChangeLog:

	* parse/rust-parse-impl.h (Parser::left_denotation): Remove
	usage of parse_tuple_index_expr_float.
	(Parser::parse_closure_expr_pratt): Remove function.

gcc/testsuite/ChangeLog:

	* rust/compile/parse_float_dot.rs: New test.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>