[infra] Remove arm32 from gcc builder.

Bug: https://github.com/dart-lang/sdk/issues/52080
Change-Id: I8332638ebb758507403b098f463291fd19f231e3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/299240
Reviewed-by: Alexander Thomas <athom@google.com>

tools/bots/test_matrix.json

@@ -1592,18 +1592,6 @@
             "runtime_precompiled"
           ]
         },
-        {
-          "name": "build dart debug arm",
-          "script": "tools/build.py",
-          "arguments": [
-            "--mode=debug",
-            "--arch=arm",
-            "--no-clang",
-            "--no-goma",
-            "runtime",
-            "runtime_precompiled"
-          ]
-        },
         {
           "name": "build dart debug riscv64",
           "script": "tools/build.py",
@@ -1639,18 +1627,6 @@
             "runtime_precompiled"
           ]
         },
-        {
-          "name": "build dart release arm",
-          "script": "tools/build.py",
-          "arguments": [
-            "--mode=release",
-            "--arch=arm",
-            "--no-clang",
-            "--no-goma",
-            "runtime",
-            "runtime_precompiled"
-          ]
-        },
         {
           "name": "build dart release riscv64",
           "script": "tools/build.py",