Remove Hamamura-san from maintainer lists (Qiskit#12115)

With Hamamura-san having moved on from IBM now, this commit removes him
from being tagged/mentioned as a primary contact/reviewer for the
modules he'd previously been working in.  We're of course happy to keep
working together, just there's no expectation anymore!

.github/CODEOWNERS

@@ -24,7 +24,7 @@
 
 # Qiskit folders (also their corresponding tests)
 providers/            @Qiskit/terra-core @jyu00
-quantum_info/         @Qiskit/terra-core @ikkoham
+quantum_info/         @Qiskit/terra-core
 qpy/                  @Qiskit/terra-core
 pulse/                @Qiskit/terra-core @eggerdj @wshanks
 synthesis/            @Qiskit/terra-core @alexanderivrii @ShellyGarion

qiskit_bot.yaml

@@ -18,13 +18,10 @@ notifications:
         - "`@nkanazawa1989`"
     "two_qubit_decompose":
         - "`@levbishop`"
-    "quantum_info":
-        - "`@ikkoham`"
     "circuit/library":
         - "`@Cryoris`"
         - "`@ajavadia`"
     "primitives":
-        - "`@ikkoham`"
         - "`@t-imamichi`"
         - "`@ajavadia`"
         - "`@levbishop`"