RISC-V: Don't decrement pc after break.

RISC-V: Don't decrement pc after break.

	gdb/
	* riscv-tdep.c (riscv_has_feature): Delete comment that refers to
	set_gdbarch_decr_pc_after_break.  Call riscv_read_misa_reg always.
	(riscv_gdbarch_init): Delete local has_compressed_isa.  Delete now
	unecessary braces after EF_RISCV_RVC test.  Delete call to
	set_gdbarch_decr_pc_after_break.