[SYCL][Doc] Update SYCL_ENABLE_DEFAULT_CONTEXTS description (#19277)

It was enabled by default on Windows long time ago:
491e6e4

Author: againull

sycl/doc/EnvironmentVariables.md

@@ -20,7 +20,7 @@ compiler and runtime.
 | `SYCL_CACHE_THRESHOLD` | Positive integer | Persistent cache eviction threshold in days (default value is 7 for 1 week). Set to 0 for disabling time-based cache eviction. |
 | `SYCL_CACHE_MIN_DEVICE_IMAGE_SIZE` | Positive integer | Minimum size of device code image in bytes which is reasonable to cache on disk because disk access operation may take more time than do JIT compilation for it. Applicable only for persistent cache. Default value is 0 to cache all images. |
 | `SYCL_CACHE_MAX_DEVICE_IMAGE_SIZE` | Positive integer | Maximum size of device image in bytes which is cached. Caching big kernels may overload the disk very fast. Applicable only for persistent cache. Default value is 1 GB. |
-| `SYCL_ENABLE_DEFAULT_CONTEXTS` | '1' or '0' | Enable ('1') or disable ('0') creation of default platform contexts in SYCL runtime. The default context for each platform contains all devices in the platform. Refer to [Platform Default Contexts](extensions/supported/sycl_ext_oneapi_default_context.asciidoc) extension to learn more. Enabled by default on Linux and disabled on Windows. |
+| `SYCL_ENABLE_DEFAULT_CONTEXTS` | '1' or '0' | Enable ('1') or disable ('0') creation of default platform contexts in SYCL runtime. The default context for each platform contains all devices in the platform. Refer to [Platform Default Contexts](extensions/supported/sycl_ext_oneapi_default_context.asciidoc) extension to learn more. Enabled by default. |
 | `SYCL_RT_WARNING_LEVEL` | Positive integer | The higher warning level is used the more warnings and performance hints the runtime library may print. Default value is '0', which means no warning/hint messages from the runtime library are allowed. The value '1' enables performance warnings from device runtime/codegen. The values greater than 1 are reserved for future use. |
 | `SYCL_USM_HOSTPTR_IMPORT` | Integer | Enable by specifying non-zero value. Buffers created with a host pointer will result in host data promotion to USM, improving data transfer performance. To use this feature, also set SYCL_HOST_UNIFIED_MEMORY=1. |
 | `SYCL_EAGER_INIT` | Integer | Enable by specifying non-zero value. Tells the SYCL runtime to do as much as possible initialization at objects construction as opposed to doing lazy initialization on the fly. This may mean doing some redundant work at warmup but ensures fastest possible execution on the following hot and reportable paths. It also instructs UR adapters to do the same. Default is "0".  |