clk: renesas: rcar-gen4: Remove unused variable PLL2 clock type

The variable PLL2 clock type was superseded by the more generic
variable fractional 8.25 PLL clock type, and its sole user was converted.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/8e5564958002351f29435f63de1304fb3b51a725.1721648548.git.geert+renesas@glider.be