tests: Remove long/nightly X86 Boot tests

The long/nightly tests are failing due to timeout (e.g.,:
https://jenkins.gem5.org/job/nightly/398/). We must therefore be more
careful about what we test on a nightly basis.

Each of these X86 boot tests takes an hour and, generally, are largely
the same (just with different CPU cores, cache hierarchy, and memory
system). Given this is largely redundant, some of these tests have been
remove dto save on testing time.

Change-Id: I761fca1aa5e111a03183f83d4e326aaea1bdbc3a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65192
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

tests/gem5/x86-boot-tests/test_linux_boot.py

@@ -150,39 +150,13 @@ test_boot(
 
 #### The long (Nightly) tests ####
 
-test_boot(
-    cpu="atomic",
-    num_cpus=1,
-    mem_system="classic",
-    memory_class="SingleChannelHBM",
-    boot_type="init",
-    length=constants.long_tag,
-)
 
 test_boot(
     cpu="timing",
     num_cpus=1,
     mem_system="mesi_two_level",
     memory_class="DualChannelDDR3_1600",
-    boot_type="init",
-    length=constants.long_tag,
-)
-
-test_boot(
-    cpu="timing",
-    num_cpus=1,
-    mem_system="mi_example",
-    memory_class="DualChannelDDR3_2133",
-    boot_type="init",
-    length=constants.long_tag,
-)
-
-test_boot(
-    cpu="timing",
-    num_cpus=4,
-    mem_system="classic",
-    memory_class="DualChannelDDR3_2133",
-    boot_type="init",
+    boot_type="systemd",
     length=constants.long_tag,
 )
 
@@ -209,14 +183,6 @@ test_boot(
 #    length=constants.long_tag,
 # )
 
-test_boot(
-    cpu="atomic",
-    num_cpus=4,
-    mem_system="classic",
-    memory_class="HBM2Stack",
-    boot_type="systemd",
-    length=constants.long_tag,
-)
 
 #### The very-long (Weekly) tests ####