ULP: remove deprecated cycle_sel field from ADC instruction

Cycle_sel field was never used in binutils and was always set to zero.
This change removes it from documentation and examples.

Needs ULP binutils with this change:
https://github.com/espressif/binutils-esp32ulp/commit/af79434

docs/api-guides/ulp_instruction_set.rst

@@ -651,21 +651,21 @@ Similar considerations apply to ``LD`` and ``ST`` instructions. Consider the fol
 ---------------------------------
 
 **Syntax**
-  **ADC**   *Rdst, Sar_sel, Mux, Cycles*
+  - **ADC**   *Rdst, Sar_sel, Mux*
+
+  - **ADC**   *Rdst, Sar_sel, Mux, 0* — deprecated form
 
 **Operands**
-  - *Rdst* –      Destination Register R[0..3], result will be stored to this register
-  - *Sar_sel* – selected ADC : 0=SARADC0, 1=SARADC1
+  - *Rdst* – Destination Register R[0..3], result will be stored to this register
+  - *Sar_sel* – Select ADC: 0 = SARADC1, 1 = SARADC2
   - *Mux*  -  selected PAD, SARADC Pad[Mux+1] is enabled
-  - *Cycle* – number of cycles used to perform measurement
 
 **Description**
   The instruction makes measurements from ADC.
 
 **Examples**::
 
-   1:        ADC      R1, 0, 1, 100 // Measure value using ADC1 pad 2,
-                                    // for 100 cycles and move result to R1
+   1:        ADC      R1, 0, 1      // Measure value using ADC1 pad 2 and store result into R1
 
 
 **REG_RD** – read from peripheral register

examples/system/ulp_adc/main/ulp/adc.S

@@ -72,7 +72,7 @@ entry:
 	stage_rst
 measure:
 	/* measure and add value to accumulator */
-	adc r1, 0, adc_channel + 1, 0
+	adc r1, 0, adc_channel + 1
 	add r0, r0, r1
 	/* increment loop counter and check exit condition */
 	stage_inc 1