Remove invalid link (Qiskit#1445) (Qiskit#1452)

Our CI can't run on forks so making a PR from within the repo.

Co-authored-by: Abdón Rodríguez <a@abdonrd.com>

tutorials/explore-composer/explore-composer.ipynb

@@ -652,7 +652,7 @@
     "\n",
     "Also known as the square-root NOT gate.\n",
     "\n",
-    "This gate implements the square-root of X, $\\sqrt{X}$. Applying this gate twice in a row produces the standard Pauli-X gate ([NOT gate](operations_glossary#not-gate)). Like the Hadamard gate, $\\sqrt{X}$ creates an equal superposition state if the qubit is in the state $|0\\rangle$, but with a different relative phase. On some hardwares, it is a native gate that can be implemented with a $\\pi/2$ or X90 pulse.\n",
+    "This gate implements the square-root of X, $\\sqrt{X}$. Applying this gate twice in a row produces the standard Pauli-X gate (NOT gate). Like the Hadamard gate, $\\sqrt{X}$ creates an equal superposition state if the qubit is in the state $|0\\rangle$, but with a different relative phase. On some hardwares, it is a native gate that can be implemented with a $\\pi/2$ or X90 pulse.\n",
     "\n",
     "| Composer reference                                | OpenQASM reference | Q-Sphere | Note about q-sphere representations                                                                                                                                                                                                     |\n",
     "| ------------------------------------------------- | ------------------ | ---------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n",
@@ -662,7 +662,7 @@
     "\n",
     "Also known as the SXdg or square-root NOT-dagger gate.\n",
     "\n",
-    "This is the inverse of the $\\sqrt{X}$ gate. Applying it twice in a row produces the Pauli-X gate ([NOT gate](operations_glossary#not-gate)), since the NOT gate is its own inverse. Like the $\\sqrt{X}$ gate, this gate can be used to create an equal superposition state, and it too is natively implemented on some hardwares using an X90 pulse.\n",
+    "This is the inverse of the $\\sqrt{X}$ gate. Applying it twice in a row produces the Pauli-X gate (NOT gate), since the NOT gate is its own inverse. Like the $\\sqrt{X}$ gate, this gate can be used to create an equal superposition state, and it too is natively implemented on some hardwares using an X90 pulse.\n",
     "\n",
     "| Composer reference                                    | OpenQASM reference | Q-Sphere | Note about q-sphere representations                                                                                                                                                                                                     |\n",
     "| ----------------------------------------------------- | ------------------ | ---------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n",