ext4: cleanup fast commit mount options

Drop no_fc mount option that disable fast commit even if it was
enabled at mkfs time. Move fc_debug_force mount option under ifdef
EXT4_DEBUG to annotate that this is strictly for debugging and testing
purposes and should not be used in production.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20201106035911.1942128-23-harshadshirwadkar@gmail.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>