Revert "ramips: add support for kernel 5.10"

This reverts commit b4aad29a1d.

This was accidentally folded into a single commit. Remove it and
apply it properly again.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/ramips/patches-5.10/324-mt7621-perfctr-fix.patch

@@ -1,15 +0,0 @@
---- a/arch/mips/ralink/irq-gic.c
-+++ b/arch/mips/ralink/irq-gic.c
-@@ -13,6 +13,12 @@
- 
- int get_c0_perfcount_int(void)
- {
-+	/*
-+	 * Performance counter events are routed through GIC.
-+	 * Prevent them from firing on CPU IRQ7 as well
-+	 */
-+	clear_c0_status(IE_SW0 << 7);
-+
- 	return gic_get_c0_perfcount_int();
- }
- EXPORT_SYMBOL_GPL(get_c0_perfcount_int);