support/config-fragments: remove nios2 toolchain

The nios2 architecture was deprecated in gcc-14 and has been removed
in the upcoming gcc-15 [1][2].

Our last and only nios2 defconfig "qemu_nios2_10m50_defconfig" was
removed in 2024.11 due to nios2 removal from Qemu 9.1.0 [3].

Remove nios2 testing from Buildroot autobuilders.

[1] https://sourceware.org/pipermail/binutils/2024-April/133675.html
[2] https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=e876acab6cdd84bb2b32c98fc69fb0ba29c81153
[3] f96b4c176f6e9d6c4374a0d322de672bf44c35bf

Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Julien Olivain <ju.o@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Julien Olivain <ju.o@free.fr>

support/config-fragments/autobuild/bootlin-nios2-glibc.config

@@ -1,4 +0,0 @@
-BR2_nios2=y
-BR2_TOOLCHAIN_EXTERNAL=y
-BR2_TOOLCHAIN_EXTERNAL_BOOTLIN=y
-BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_NIOS2_GLIBC_STABLE=y

support/config-fragments/autobuild/toolchain-configs.csv

@@ -28,7 +28,6 @@ support/config-fragments/autobuild/bootlin-m68k-5208-uclibc.config,x86_64
 support/config-fragments/autobuild/bootlin-microblazeel-uclibc.config,x86_64
 support/config-fragments/autobuild/bootlin-mipsel-uclibc.config,x86_64
 support/config-fragments/autobuild/bootlin-mipsel32r6-glibc.config,x86_64
-support/config-fragments/autobuild/bootlin-nios2-glibc.config,x86_64
 support/config-fragments/autobuild/bootlin-openrisc-uclibc.config,x86_64
 support/config-fragments/autobuild/bootlin-powerpc64le-power8-glibc.config,x86_64
 support/config-fragments/autobuild/bootlin-powerpc-e500mc-uclibc.config,x86_64