build: reduce targets list for faster testbuildbot builds

.buildconf/targets-testbuildbot.txt

@@ -1,32 +1,6 @@
 # Generated by 'openwrt.git/scripts/dump-target-info.pl architectures'
-aarch64_cortex-a53 bcm27xx/bcm2710 bcm4908/generic mediatek/mt7622 mediatek/filogic mvebu/cortexa53 qualcommax/ipq807x sunxi/cortexa53
-aarch64_cortex-a72 bcm27xx/bcm2711 mvebu/cortexa72
-aarch64_generic armsr/armv8 layerscape/armv8_64b octeontx/generic rockchip/armv8
-arm_arm1176jzf-s_vfp bcm27xx/bcm2708
-arm_arm926ej-s at91/sam9x mxs/generic
-arm_cortex-a15_neon-vfpv4 armsr/armv7 ipq806x/generic ipq806x/chromium
-arm_cortex-a5_vfpv4 at91/sama5
-arm_cortex-a7 mediatek/mt7629
-arm_cortex-a7_neon-vfpv4 bcm27xx/bcm2709 imx/cortexa7 ipq40xx/generic ipq40xx/chromium ipq40xx/mikrotik layerscape/armv7 mediatek/mt7623 sunxi/cortexa7
-arm_cortex-a7_vfpv4 at91/sama7
-arm_cortex-a8_vfpv3 sunxi/cortexa8
-arm_cortex-a9 bcm53xx/generic
-arm_cortex-a9_neon imx/cortexa9 zynq/generic
-arm_cortex-a9_vfpv3-d16 mvebu/cortexa9 tegra/generic
-arm_fa526 gemini/generic
-arm_mpcore oxnas/ox820
-arm_xscale kirkwood/generic
-i386_pentium-mmx x86/legacy x86/geode
-i386_pentium4 x86/generic
-mips64_octeonplus octeon/generic
-mips_24kc ath79/generic ath79/mikrotik ath79/nand ath79/tiny lantiq/xway lantiq/xway_legacy malta/be realtek/rtl839x realtek/rtl930x realtek/rtl931x
-mips_4kec realtek/rtl838x
-mips_mips32 bmips/bcm6318 bmips/bcm6328 bmips/bcm6358 bmips/bcm6362 bmips/bcm6368 bmips/bcm63268 lantiq/ase
-mipsel_24kc ramips/mt7620 ramips/mt7621 ramips/mt76x8 ramips/rt288x ramips/rt305x
-mipsel_24kc_24kf pistachio/generic
-mipsel_74kc bcm47xx/mips74k ramips/rt3883
-mipsel_mips32 bcm47xx/generic bcm47xx/legacy
-powerpc_464fp apm821xx/nand apm821xx/sata
-powerpc_8548 mpc85xx/p1010 mpc85xx/p1020 mpc85xx/p2020
-riscv64_riscv64 sifiveu/generic
+aarch64_generic armsr/armv8
+arm_cortex-a7_neon-vfpv4 ipq40xx/generic ipq40xx/mikrotik
+mips_24kc ath79/tiny
+mipsel_24kc ramips/mt7621
 x86_64 x86/64