Remove unused slider component (#12303)

It is unused as of https://github.com/matrix-org/matrix-react-sdk/pull/12246. I noticed this while working on https://github.com/matrix-org/matrix-react-sdk/pull/12299.

src/components/views/elements/Slider.tsx

@@ -1,88 +0,0 @@
-/*
-Copyright 2020 The Matrix.org Foundation C.I.C.
-
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-    http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
-*/
-
-import * as React from "react";
-import { ChangeEvent } from "react";
-
-interface IProps {
-    // A callback for the selected value
-    onChange: (value: number) => void;
-
-    // The current value of the slider
-    value: number;
-
-    // The min and max of the slider
-    min: number;
-    max: number;
-    // The step size of the slider, can be a number or "any"
-    step: number | "any";
-
-    // A function for formatting the values
-    displayFunc: (value: number) => string;
-
-    // Whether the slider is disabled
-    disabled: boolean;
-
-    label: string;
-}
-
-const THUMB_SIZE = 2.4; // em
-
-export default class Slider extends React.Component<IProps> {
-    private get position(): number {
-        const { min, max, value } = this.props;
-        return Number(((value - min) * 100) / (max - min));
-    }
-
-    private onChange = (ev: ChangeEvent<HTMLInputElement>): void => {
-        this.props.onChange(parseInt(ev.target.value, 10));
-    };
-
-    public render(): React.ReactNode {
-        let selection: JSX.Element | undefined;
-
-        if (!this.props.disabled) {
-            const position = this.position;
-            selection = (
-                <output
-                    className="mx_Slider_selection"
-                    style={{
-                        left: `calc(2px + ${position}% + ${THUMB_SIZE / 2}em - ${(position / 100) * THUMB_SIZE}em)`,
-                    }}
-                >
-                    <span className="mx_Slider_selection_label">{this.props.value}</span>
-                </output>
-            );
-        }
-
-        return (
-            <div className="mx_Slider">
-                <input
-                    type="range"
-                    min={this.props.min}
-                    max={this.props.max}
-                    value={this.props.value}
-                    onChange={this.onChange}
-                    disabled={this.props.disabled}
-                    step={this.props.step}
-                    autoComplete="off"
-                    aria-label={this.props.label}
-                />
-                {selection}
-            </div>
-        );
-    }
-}