Revert "pika: Add conflict between HIP and GCC (libstdc++) >= 13 (#46291)" (#48693)

The conflict is too strict and prevents usable combinations from being
concretized. Some packages depend on pika, but do not include pika
headers in HIP device code files, and can thus be compiled even with the
bad combination of HIP and GCC versions.

var/spack/repos/builtin/packages/pika/package.py

@@ -149,8 +149,6 @@ class Pika(CMakePackage, CudaPackage, ROCmPackage):
     depends_on("apex", when="+apex")
     depends_on("cuda@11:", when="+cuda")
     depends_on("hip@5.2:", when="@0.8: +rocm")
-    # https://github.com/pika-org/pika/issues/1238
-    conflicts("%gcc@13:", when="+rocm")
     depends_on("hipblas", when="@:0.8 +rocm")
     depends_on("mpi", when="+mpi")
     with when("+stdexec"):