ramips/mt7621: drop the timer recalibration patch

ramips/mt7621: drop the timer recalibration patch

We've been carrying this patch for many years [1], in order to fix a timer
calibration issue on MT7621. Turns out, after retesting with a recent kernel
(Linux 5.10), the system works perfectly fine without it (no rcu_sched stalls
or inconsistent BogoMIPS values across CPUs).

Manually refreshed:
322-mt7621-fix-cpu-clk-add-clkdev.patch
323-mt7621-memory-detect.patch

[1] https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=6f4a903533361a2906a4d94ac6f597cd9c6c47bc

Suggested-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
Tested-by: Donald Hoskins <grommish@gmail.com>
Signed-off-by: Rui Salvaterra <rsalvaterra@gmail.com>